Atoms and Molecules Online Test 10th Science Lesson 7 Questions in English

Atoms and Molecules Online Test 10th Science Lesson 7 Questions in English

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Question 1
  • Assertion (A): The Greek philosophers first proposed the idea of atom in fifth century BCE.
  • Reasoning(R): The Greek theory of atom was more philosophical than scientific.
A
Both A and R is True and R is the correct explanation of A.
B
Both A and R is True but R is not the correct explanation of A.
C
A is True but R is False.
D
Both A and R is False.
Question 1 Explanation: 
Matter is made of atoms. Curiously the idea of atom was first proposed by the Greek philosophers in the fifth century BC (BCE). But their theory was more philosophical than scientific.
Question 2
Who proposed the first scientific theory of atom?
A
John Dalton
B
Ernest Rutherford
C
Robert Boyle
D
William Ramsay
Question 2 Explanation: 
The first scientific theory of the atom was proposed by John Dalton.
Question 3
Which of this scientist did not agree with Dalton’s theory?
A
J.J. Thomson
B
Rutherford
C
Neil’s Bohr
D
All the above
Question 3 Explanation: 
Few of the postulates of Dalton’s theory about an atom were found incorrect by the later on studies made by J.J. Thomson, Rutherford, Neil’s Bohr and Schrodinger.
Question 4
Define Isobar.
A
Atoms of same element and same atomic mass.
B
Atoms of different element and different atomic mass.
C
Atoms of same element and different atomic mass.
D
Atoms of different element and same atomic mass.
Question 4 Explanation: 
Atoms of the same element may have different atomic mass. (Discovery of isotopes 17Cl35, 17Cl37). Atoms of different elements may have same atomic masses (discovery of Isobars 18Ar40, 20Ca40).
Question 5
Which of this concept describe the indestructible nature of an atom?
A
Isotopes
B
Artificial Transmutation
C
Isomer
D
Isobar
Question 5 Explanation: 
Atoms of one element can be transmuted into atoms of other elements. In other words, atom is no longer indestructible (discovery of artificial transmutation).
Question 6
What is the chemical composition of the natural honey?
  1. C6H12 O6
  2. C4H10O2
  3. C12H20O6
  4. C1H4O4
A
A
B
B
C
C
D
D
Question 6 Explanation: 
Atoms may not always combine in a simple whole number ratio (E.g. Glucose C6H12O6 C:H:O = 6:12:6 or 1:2:1 and Sucrose C12H22O11 C:H:O = 12:22:11).
Question 7
In which of this smallest particle a chemical reaction occurs?
A
Atoms
B
Molecules
C
Protons
D
Molar
Question 7 Explanation: 
Atom is the smallest particle that takes part in a chemical reaction. The mass of an atom can be converted into energy (E = mc2).
Question 8
What is defined as mass number of an atom?
A
Sum of number of protons and neutrons
B
Sum of number of neutrons
C
Sum of number of electrons and protons
D
Sum of number of electrons
Question 8 Explanation: 
Protons and neutrons have considerable mass, but electrons don't have such a considerable mass. Thus, the mass of an atom is mainly contributed by its protons and neutrons and hence the sum of the number of protons and neutrons of an atom is called its mass number.
Question 9
Which of these is used to measure the mass of an atom?
A
Mass number
B
Milligram
C
Atomic mass unit
D
Nanometer
Question 9 Explanation: 
Individual atoms are very small and it is difficult to measure their masses. You can measure the mass of macroscopic materials in gram or kilogram. The mass of an atom is measured in atomic mass unit (amu).
Question 10
What is the approximate mass of a proton or neutron?
A
10 amu
B
1 amu
C
100 amu
D
0.01 amu
Question 10 Explanation: 
The mass of a proton or neutron is approximately 1 amu.
Question 11
Which of this symbol is used to denote the unified atomic mass in the modern system?
A
A
B
U
C
M
D
Au
Question 11 Explanation: 
The symbol ‘amu’ is no longer used in the modern system and instead it uses the symbol ‘U’ to denote unified atomic mass.
Question 12
  • Assertion (A): Relative mass was used to measure the atomic mass by elements of equal number of atoms.
  • Reasoning(R): The absolute mass of an atom cannot be determined directly.
A
Both A and R is True and R is the correct explanation of A.
B
Both A and R is True but R is not the correct explanation of A.
C
A is True but R is False.
D
Both A and R is False.
Question 12 Explanation: 
As an atom is very small, its absolute mass cannot be determined directly. The early pioneers of chemistry used to measure the atomic mass of an atom relative to an atom of another element. They measured the masses of equal number of atoms of two or more elements at a time, to determine their relative masses.
Question 13
Which of these is used as a standard for measuring atomic mass?
A
A standard element
B
Planks constant
C
Atmospheric pressure
D
Standard temperature
Question 13 Explanation: 
The established one element as a standard, gave it an arbitrary value of atomic mass and using this value they measured the relative mass of other elements. The mass obtained by this way is called relative atomic mass.
Question 14
Which of this carbon isotope is used as standard measure for relative atomic mass?
A
C-17
B
C-19
C
C-12
D
C-15
Question 14 Explanation: 
Later hydrogen atom was replaced by oxygen atom as the standard. Now the stable isotope of carbon (C-12) with atomic mass 12 is used as the standard for measuring the relative atomic mass of an element.
Question 15
  • Assertion (A): All the Atoms are indivisible.
  •    Reasoning(R): An atom is made up of protons, neutrons and electrons.
A
Both A and R is True and R is the correct explanation of A.
B
Both A and R is True but R is not the correct explanation of A.
C
A is False but R is True.
D
Both A and R is False.
Question 15 Explanation: 
‘The main postulates of modern atomic theory’ are as follows: An atom is no longer indivisible (after the discovery of the electron, proton, and neutron).
Question 16
Which of the following is not a subatomic particle?
A
Proton
B
Neutron
C
Molecule
D
Electron
Question 16 Explanation: 
Atoms are the building blocks of matter. Since matter has mass, it must be due to its atoms. According to the modern atomic theory, an atom contains subatomic particles such as protons, neutrons and electrons.
Question 17
Which of the following is not true regarding the atomic mass unit?
A
One-twelfth of mass of a Carbon-12 atom.
B
Carbon-12 is an isobar of carbon.
C
Carbon-12 contains 6 protons and 6 neutrons.
D
Carbon-12 is an isotope of carbon.
Question 17 Explanation: 
Atomic mass unit is one-twelfth of the mass of a carbon-12 atom; an isotope of carbon, which contains 6 protons and 6 neutrons.
Question 18
Which of the atom is not a standard mass for relative atomic mass?
A
Hydrogen
B
Oxygen
C
Carbon
D
Helium
Question 18 Explanation: 
The mass of hydrogen atom was chosen as a standard and masses of other atoms were compared with it because of the existence of isotopic character of hydrogen (1H1, 1H2, 1H3).
Question 19
What is defined as mass nuAtoms are the building blocks of matter. Since matter has mass, it must be due to its atoms. According to the modern atomic theory, an atom contains subatomic particles such as protons, neutrons and electrons.  mber of an atom?
A
Sum of number of protons and neutrons
B
Sum of number of neutrons
C
Sum of number of electrons and protons
D
Sum of number of electrons
Question 19 Explanation: 
Protons and neutrons have considerable mass, but electrons don't have such a considerable mass. Thus, the mass of an atom is mainly contributed by its protons and neutrons and hence the sum of the number of protons and neutrons of an atom is called its mass number.
Question 20
Choose the Incorrect statements regarding relative atomic mass.
  1. 1/10 th part of mass of a carbon-12 atom.
  2. Denoted by Ar.
  3. Also known as Standard Atomic Weight.
A
i only
B
ii only
C
iii only
D
None of the above
Question 20 Explanation: 
Relative atomic mass of an element is the ratio between the average mass of its isotopes to 1/ 12th part of the mass of a carbon-12 atom. It is denoted as Ar. It is otherwise called “Standard Atomic Weight”.
Question 21
What is defined as relative atomic mass?
A
Ratio between Average mass of isotopes and mass of carbon atom.
B
Ratio of Total number of isotopes of element to the mass of carbon.
C
Average mass of carbon atoms
D
Ratio of Average mass of isotopes of the element and 1/12th of mass of carbon-12 atom.
Question 22
State the modern method of determining atomic mass?
A
Vernier caliper
B
Mass Spectrometry
C
Physical Balance
D
Standard Elements
Question 22 Explanation: 
Modern methods of determination of atomic mass are done by Mass Spectrometry which uses C-12 as standard.
Question 23
Which of the given element has relative atomic mass value as one?
A
Hydrogen
B
Sulphur
C
Sodium
D
Nitrogen
Question 24
Identify the incorrect match.
  1. O          i) 16
  2. Mg      ii) 24
  3. N        iii) 10
  4. C         iv) 12
A
i only
B
ii only
C
iii only
D
iv only
Question 25
What is the unit of relative atomic mass?
A
No unit
B
Grams
C
amu
D
None of the above
Question 25 Explanation: 
Relative Atomic Mass is only a ratio so it has no unit. If the atomic mass of an element is expressed in grams it is called as Gram Atomic Mass.
Question 26
What is the gram atomic mass of nitrogen?
A
1g
B
16g
C
12g
D
14g
Question 26 Explanation: 
Gram Atomic Mass of hydrogen = 1 g Gram Atomic Mass of carbon = 12 g Gram Atomic Mass of nitrogen = 14 g Gram Atomic Mass of oxygen = 16 g
Question 27
  • Assertion (A): The isotopic mixture of elements is considered to calculate the atomic mass of an element.
  • Reasoning(R): Naturally occurring element exists as a mixture of isotopes with their own mass.
A
Both A and R is True and R is the correct explanation of A.
B
Both A and R is True but R is not the correct explanation of A.
C
A is True but R is False.
D
Both A and R is False.
Question 27 Explanation: 
It is somewhat more complicated because most of the naturally occurring elements exist as a mixture of isotopes each of which has its own mass. Thus it is essential to consider this isotopic mixture while calculating the atomic mass of an element.
Question 28
Which of the following is used to measure the average atomic mass of an element?
A
Natural isotopes
B
Chemical reactions
C
Available compounds
D
All the above
Question 28 Explanation: 
The average atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes.
Question 29
Calculate the average atomic mass of an element having 2 isotopes of 75% and 25% with masses 10, 20 respectively?
A
25
B
10.5
C
100
D
12.5
Question 29 Explanation: 
Average atomic mass = (Mass of 1st isotope × % abundance of 1st isotope) + (Mass of 2nd isotope ×% abundance of 2nd isotope) Thus for the given element the average atomic mass = (10 × 75 / 100) + (20 × 25 / 100) = 12.5
Question 30
Choose the correct statements.
  1. Atomic weight is also used as Average atomic mass.
  2. Atomic mass of all the elements is whole numbers.
A
i only
B
ii only
C
Both i and ii
D
Neither i nor ii
Question 30 Explanation: 
The atomic masses of elements given in the periodic table are average atomic masses. Sometimes the term atomic weight is used to mean average atomic mass. It is observed from the periodic table that atomic masses of most of the elements are not whole numbers.
Question 31
Which of these carbon isotopes are considered for calculating the atomic mass of carbon?
A
C-12, C-9
B
C-11, C-7
C
C-12, C-13
D
C-5, C-17
Question 31 Explanation: 
To calculate the atomic mass of carbon both of its natural isotopes such as carbon-12 and carbon-13 are considered. The natural abundance of C-12 and C-13 are 98.90 % and 1.10 % respectively. The average of the atomic mass of carbon is calculated as follows:Average atomic mass of carbon = (12 × 9 8 . 9 ) 100 + (13 × ) 1.1 100
Question 32
Match the atomic mass and its elements.
  1. Lithium              i) 1.008
  2. Hydrogen         ii) 4.003
  3. Boron               iii) 6.941
  4. Helium             iv) 10.811
A
ii, iv, i, iii
B
iii, i, iv, ii
C
ii, iii, i, iv
D
iv, i, iii, ii
Question 33
Which of this Oxygen isotope is abundantly available in nature?
  1. 8O16
  2. 5O11
  3. 8O17
  4. 8O15
A
A
B
B
C
C
D
D
Question 33 Explanation: 
Isotopes of oxygen
Question 34
Which of this element is not found as single atom by nature?
A
Helium
B
Argon
C
Fluorine
D
Xenon
Question 34 Explanation: 
Except noble gases atoms of most of the elements are found in the combined form with itself or atoms of other elements. It is called as a molecule.
Question 35
Define a molecule.
A
Combination of two atoms only.
B
Physical attraction of atoms.
C
Combination of two or more atoms.
D
None of the above.
Question 35 Explanation: 
A molecule is a combination of two or more atoms held together by strong chemical forces of attraction, i.e. chemical bonds.
Question 36
  • Assertion (A): A molecule may be an element or a compound.
  • Reasoning(R): Molecules may contain atoms of same element or two or more elements.
A
Both A and R is True and R is the correct explanation of A.
B
Both A and R is True but R is not the correct explanation of A.
C
A is True but R is False.
D
Both A and R is False.
Question 36 Explanation: 
A molecule may contain atoms of the same element or may contain atoms of two or more elements joined in a fixed ratio, in accordance with the law of definite proportions. Thus, a molecule may be an element or a compound.
Question 37
Which of the following denotes a homoatomic molecule?
A
Similar kind of atoms
B
Single atom element
C
Simple chemical reaction
D
Similar atomic value
Question 37 Explanation: 
If the molecule is made of similar kind of atoms, then it is called homoatomic molecule.
Question 38
  • Assertion (A): Heteroatomic molecule consists of atoms of different elements.
  • Reasoning(R):  A compound is also referred as a heteroatomic molecule.
A
Both A and R is True and R is the correct explanation of A.
B
Both A and R is True but R is not the correct explanation of A.
C
A is True but R is False.
D
Both A and R is False.
Question 38 Explanation: 
The molecule that consists of atoms of different elements is called heteroatomic molecule. A compound is a heteroatomic molecule.
Question 39
What is referred as atomicity?
A
Total number of molecules
B
Number of free electrons
C
Number of atoms in a molecule
D
Number of chemical forces connecting atoms.
Question 39 Explanation: 
The number of atoms present in the molecule is called its ‘atomicity’.
Question 40
How many number of atoms are present in polyatomic elements?
A
=3
B
<3
C
> 3
D
All the above
Question 41
Ozone,
  1. Has three oxygen molecules.
  2.  It is a homotriatomic molecule.
  3.  It is also called as polyatomic molecule.
A
i only
B
ii only
C
iii only
D
All the above
Question 41 Explanation: 
Ozone (O3) contains three oxygen atoms and hence it is called homotriatomic molecule. If a molecule contains more than three atoms, then it is called polyatomic molecule.
Question 42
A Heterodiatomic molecule,
A
Consists of two atoms
B
Consists of same element atoms
C
Atomicity value is one.
D
Two atoms of different elements.
Question 42 Explanation: 
Consider hydrogen chloride. It consists of two atoms, but of different elements, i.e. hydrogen and chlorine. So, its atomicity is two. It is a heterodiatomic molecule.
Question 43
What is the atomicity value of the water molecule?
A
2
B
3
C
4
D
1
Question 43 Explanation: 
The water molecule contains two hydrogen atoms and one oxygen atom. So its atomicity is three. It is a heterotriatomic molecule.
Question 44
Which of this carbon isotope is used to calculate the relative molecular mass of a molecule?
A
C-12
B
C-10
C
C-9
D
C-17
Question 44 Explanation: 
The Relative Molecular Mass of a molecule is the ratio between the mass of one molecule of the substance to 1 /12th mass of an atom of Carbon -12.
Question 45
What is the relative molecular mass of water?
A
18
B
12
C
10
D
3
Question 45 Explanation: 
Relative molecular mass of water (H2O) is calculated as follows: A water molecule is made of 2 atoms of hydrogen and one atom of oxygen. So, the relative molecular mass of water = (2 × mass of hydrogen) + (1 × mass of oxygen) = (2 × 1) + (1 × 16) = 18 i.e., one molecule of H2O is 18 times as heavy as 112th of the mass of a carbon –12.
Question 46
  • Assertion (A): Molecular mass of a compound in grams is called Gram molecular mass.
  • Reasoning(R): Relative Molecular mass is a ratio value expressed in grams.
A
Both A and R is True and R is the correct explanation of A.
B
Both A and R is True but R is not the correct explanation of A.
C
A is True but R is False.
D
Both A and R is False.
Question 46 Explanation: 
Relative Molecular Mass is only a ratio. So, it has no unit. If the molecular mass of a compound is expressed in grams, it is called Gram Molecular Mass.
Question 47
What is the gram molecular mass value of carbon dioxide?
A
17g
B
36.5g
C
4.4g
D
44g
Question 47 Explanation: 
Gram Molecular Mass of water = 18 g Gram Molecular Mass of carbon dioxide = 44 g Gram Molecular Mass of ammonia = 17 g Gram Molecular Mass of HCl = 36.5 g
Question 48
Choose the correct statements regarding atoms.
  1. Atom is the smallest particle of an element.
  2. Atoms have a chemical bond.
  3. All the atoms are highly reactive.
A
i only
B
ii only
C
iii only
D
All the above
Question 49
Which of these exist in a free state?
A
Atom
B
Neutron
C
Molecule
D
Proton
Question 50
Which of this statement is not correct?
A
Noble gas atoms exist in Free State.
B
Molecules are highly reactive.
C
Molecule is the smallest particle of a compound.
D
Atoms in a molecule are held by chemical bonds.
Question 51
In which of this scale the atomic mass is measured?
A
U
B
Milligrams
C
Relative scale
D
A
Question 51 Explanation: 
Atomic mass units provide a relative scale for the masses of the elements. Since the atoms have such small masses, no usable scale can be devised to weigh them in the calibrated units of atomic mass units.
Question 52
Which of these is used to denote the number of particles?
A
Mass
B
Mole
C
Numeric
D
Grams
Question 52 Explanation: 
Chemists measure atoms and molecules in ‘moles’. So you can now understand that ‘mole’ denotes a number of particles.
Question 53
Which of these entities are included in SI system calculation for a mol?
A
Atoms
B
Molecules
C
Ions
D
All the above
Question 53 Explanation: 
In the SI system, the mole (mol) is the amount of a substance that contains as many elementary entities (atoms, molecules, or other particles) as there are atoms in exactly 12 g (or 0.012 kg) of the carbon-12 isotope.
Question 54
Which of these represents the actual number of atoms in 12g of carbon-12?
A
Avogadro Number
B
Atomic Mass Number
C
Atomic Molecule Number
D
Molecule Number
Question 54 Explanation: 
The actual number of atoms in 12 g of carbon-12 is determined experimentally. This is called Avogadro’s number (NA)
Question 55
What is the value of Avogadro Number?
  1. 6.674 *10-11
  2. 6.626 *10-34
  3. 6.023 * 1023
  4. 5.6703* 10-8
A
A
B
B
C
C
D
D
Question 55 Explanation: 
NA is named after an Italian scientist Amedeo Avogadro who proposed its significance. Its value is 6.023 × 1023. So one mole of a substance contains 6.023 × 1023 entities.
Question 56
Which of these values is counted in moles?
A
Mass
B
Particles
C
Atoms
D
Molecules
Question 56 Explanation: 
Mole Concept: The study of the collection of particles by using mole as the counting unit in order to express the mass and volume of such unit particles in a bulk of matter is known as mole concept.
Question 57
Which of these data’s can be counted by the number of moles?
A
Number of moles of molecules.
B
Number of moles in a chemical reaction.
C
Number of moles of ions.
D
Number of moles of atoms.
Question 57 Explanation: 
The number of moles of a substance can be calculated by various means depending on the data available, as follows: Number of moles of molecules. Number of moles of atoms. Number of moles of a gas (Standard molar volume at STP = 22.4 litre). Number of moles of ions.
Question 58
What is the standard pressure value of a STP?
A
1.00 atm
B
10 atm
C
0.001 atm
D
100 atm
Question 58 Explanation: 
STP-Standard Temperature and Pressure (273.15 K,1.00 atm)
Question 59
Which of these given values are equal to one mole of an element?
A
Gram atomic mass
B
Relative atomic mass
C
Average atomic mass
D
Total number of isotopes
Question 59 Explanation: 
One mole of an element contains 6.023 × 1023 atoms and it is equal to its gram atomic mass .i.e., one mole of oxygen atom contains 6.023 × 1023 atoms of oxygen and its gram atomic mass is 16 g.
Question 60
What is the value of one mole of a matter?
A
6.023 * 1023
B
Avogadro Number
C
NA
D
All the above
Question 60 Explanation: 
One mole of matter contains 6.023 × 1023 molecules and it is equal to its gram molecular mass.
Question 61
How much volume does one mole of gas occupies at STP?
A
22.4 liter
B
220 ml
C
224000 liter
D
2240 ml
Question 61 Explanation: 
One mole of any gas occupies 22.4 liter or 22400 ml at S.T.P. This volume is called as molar volume.
Question 62
Which of the following is not correct regarding the number of moles calculation?
A
Mass / Average number of isotopes
B
Mass / Molecular mass
C
Number of atoms / 6.0238* 1023
D
Mass / Atomic mass
Question 62 Explanation: 
Calculation of number of moles by Different modes Number of moles = Mass / Atomic Mass = Mass / Molecular mass = Number of Atoms / 6.023 × 1023 = Number of Molecules / 6.023 × 1023
Question 63
The percentage composition represents the ____ of each element in ___ of the compound.
A
Number of molecules, 10 g
B
Number of atoms, 100g
C
Mass, 100g
D
Average mass, 10g
Question 63 Explanation: 
The percentage composition of a compound represents the mass of each element present in 100 g of the compound.
Question 64
What is the value of the mass percentage of an element?
A
Mass of element in compound / molecular mass of the compound * 100
B
Average mass value of compound / atomic mass of the element * 100
C
Mass of the compound / molecular mass of the compound * 100
D
Atomic mass value of compound / molecular value of isotopes * 100
Question 64 Explanation: 
Mass % of an element = mass of that element in the compound / molecular mass of the compound * 100 Now, molecular mass of H2O = 2(1) + 16 = 18 g Mass % of hydrogen = 2 × 100 18 = 11.11 % Mass % of oxygen = 16 × 100 18 = 88.89 % This percentage composition is useful to determine the empirical formula and molecular.
Question 65
When did Avogadro frame a hypothesis relating volume of gas and molecules?
A
1811
B
1732
C
1891
D
1632
Question 65 Explanation: 
In 1811 Avogadro framed a hypothesis based on the relationship between the numbers of molecules present in equal volumes of gases in different conditions.
Question 66
Define the Avogadro’s law?
A
Equal volume of all gas varies with unequal number of molecules.
B
Equal volume of all gas contains equal number of molecules under ideal condition.
C
Unequal volume of all gas contains equal number of molecules.
D
Under similar conditions of temperature and pressure equal volume of all gas contains equal number of molecules.
Question 66 Explanation: 
The Avogadro’s law states that “equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules”
Question 67
Which of the following represents the Avogadro law?
A
V = n
B
V α n
C
V < n
D
V > n
Question 67 Explanation: 
It follows that the volume of any given gas must be proportional to the number of molecules in it. If ‘V’ is the volume and ‘n’ is the number of molecules of a gas, then Avogadro law is represented, mathematically, as follows: V α n V = constant × n
Question 68
How many oxygen atoms are in Potassium permanganate?
A
3
B
4
C
1
D
5
Question 68 Explanation: 
The chemical formula for potassium permanganate is KMnO4 which has one potassium, one manganese and four oxygen atoms.
Question 69
Which of these is not an application of Avogadro’s law?
A
Determining the atomicity of gas.
B
Determining the average mass of all gases.
C
Relation between molecular mass and vapor density.
D
Determining gram molar volume of gas.
Question 69 Explanation: 
APPLICATIONS OF AVOGADRO’S LAW: It explains Gay-Lussac’s law. It helps in the determination of atomicity of gases. Molecular formula of gases can be derived using Avogadro’s law. It determines the relation between molecular mass and vapor density. It helps to determine gram molar volume of all gases (i.e, 22.4 liter at S.T.P)
Question 70
Which of these are not related in calculating the relative molecular mass by hydrogen scale?
A
Relative Molecular Mass of a gas
B
Mass of one molecule of a gas
C
Mass of one atom of Hydrogen
D
Average mass of isotopes
Question 70 Explanation: 
Relative molecular mass: (Hydrogen scale) The Relative Molecular Mass of a gas or vapor is the ratio between the mass of one molecule of the gas or vapor to mass of one atom of Hydrogen.
Question 71
What are the factors considered to measure the vapor density of a gas?
A
Temperature
B
Pressure
C
Viscosity
D
Both a and b
Question 71 Explanation: 
Vapor density is the ratio of the mass of a certain volume of a gas or vapor to the mass of an equal volume of hydrogen measured under the same conditions of temperature and pressure. Vapor Density (V.D.) = Mass of a given volume of gas or vapor at S.T.P. / Mass of the same volume of hydrogen
Question 72
What is the vapor density value at STP?
A
Mass of total molecules / mass of hydrogen
B
Mass of n molecules of gas / Mass of n molecules of hydrogen
C
Average molecular value of gas / Mass of hydrogen isotopes
D
Total number of isotopes / Average number of isotopes of hydrogen
Question 72 Explanation: 
V.D. at S.T.P = Mass of ‘n’ molecules of a gas or vapor at S.T.P. / Mass of ‘n’ molecules of hydrogen
Question 73
Which of the following is the value of Vapor density?
A
Relative molecular mass / 2
B
Relative molecular mass * 4
C
Relative molecular mass / 4
D
Relative molecular mass * 2
Question 73 Explanation: 
Relative molecular mass = 2 × Vapor density
Question 74
Calculate percentage of Hydrogen in H2SO4.
A
20
B
2.04
C
32
D
64
Question 74 Explanation: 
Molecular mass of H2SO4 = (1 × 2) + (32 × 1) + (16 × 4) = 2 + 32 + 64 = 98 g % of H in H2SO4 = Mass of hydrogen / Molecular mass of H2SO4 * 100 % of H in H2SO4 = 2/ 98 * 100 = 2.04
Question 75
Calculate the number of moles in 10 liter of CO2 at S.T.P.
A
0.446
B
0.23
C
2.34
D
4.4
Question 75 Explanation: 
Number of moles of CO2 = Volume at S.T.P / Molar volume = 10 / 22.4 = 0.446
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