Please refer to the MCQ Questions for Class 9 Science Chapter 3 Atoms And Molecules. The following Atoms And Molecules Class 9 Science MCQ Questions have been designed based on the latest syllabus and examination pattern for Class 9. Our experts have designed MCQ Questions for Class 9 Science with Answers for all chapters in your NCERT Class 9 Science book.
Atoms And Molecules Class 9 MCQ Questions with Answers
See below Atoms And Molecules Class 9 Science MCQ Questions, solve the questions and compare your answers with the solutions provided below.
Question. If isotopic distribution of C-12 & C-14 is 98% and 2% respectively, then number of C-14 atoms in 12 g of C is:
Question: If 12 g of carbon burns completely in 40 g oxygen in a closed container, the product has
a. 44 g of carbon dioxide
b. 8 g of oxygen
c. both a. and b.
d. none of these.
Question: Identify the incorrect statement.
a. The building blocks of all matter are atoms.
b. Atoms are very small. They cannot be seen by the naked eye.
c. The size of an atom is expressed in metres.
d. An atom of hydrogen has the radius of the order of 10–10 m.
Question: Which one of the following pair of gases contains the same number of moles?
a. 16 g of O2 and 14 g of N2
b. 8 g of O2 and 22 g of CO2
c. 28 g of N2 and 22 g of CO2
d. 32 g of O2 and 32 g of N2
Question: The number of atoms in 0.1 mole of a triatomic gas is
a. 6.026 × 1022
b. 1.806 × 1023
c. 3.6 × 1023
d. 1.8 × 1022
Question: Which of the following statements is not true about an atom?
a. Atoms are not able to exist independently.
b. Atoms are the basic units from which molecules and ions are formed.
c. Atoms are always neutral in nature.
d. Atoms aggregate in large numbers to form
the matter that we can see, feel or touch.
Question: Elements belonging to different groups of the periodic table are given below. If the element X forms a chloride whose formula is ‘XCl2’ then element ‘X’ belongs to the group whose representative element is
Question: Match List-I with List-II and mark the correct option.
(P) 0.25 mole oxygen 1. 6.022 × 1023
(Q) 18 g water 2. 1.505 × 1023
(R) 46 g Na atom 3. 6.022 × 1023 atoms
(S) 1 mole C atom 4. 12.044 × 1023 atoms
a. P-1, Q-2, R-3, S-4 b. P-2, Q-1, R-4, S-3
c. P-4, Q-1, R-3, S-2 d. P-1, Q-4, R-3, S-2
Question: Observe the given experimental set-up in which an ignition tube containing solution of X,is dipped in a conical flask containing solution of Y. Tilt and swirl the flask, so that both the solutions get mixed.
According to the law of conservation of mass, what could be solutions X and Y?
a. Copper sulphate Sodium carbonate
b. Barium chloride Sodium sulphate
c. Lead nitrate Sodium chloride
d. All of these
Question: In a science project, Aditya has to make a chart, illustrating various elements and their atomicity.
Aditya decided to show elements of different atomicity by different shapes.
Question: How many grams of H2SO4 are present in 0.25 mole of H2SO4?
Question: The mass of a molecule of water is
a. 3 × 10–26 kg
b. 3 × 10–25 kg
c. 1.5 × 10–26 kg
d. 2.5 × 10–26 kg
Question: 52 g of He contains
a. 4 × 6.022 × 1023 atoms
b. 13 atoms
c. 13 × 6.022 × 1023 atoms
d. 4 atoms
Question: Identify the correct statements.
(i) In a compound such as water, the ratio of the mass of hydrogen to the mass of oxygen is always 8 : 1.
(ii) If 9 g of water is decomposed, 1 g of hydrogen and 8 g of oxygen are always obtained.
(iii) In ammonia, nitrogen and hydrogen are always present in the ratio 3 : 14 by mass.
(iv) Many compounds are composed of two or more elements and each such compound has the same elements in the same proportions.
a. (i) and (iii)
b. (i), (ii) and (iii)
c. (ii) and (iv)
d. All of these
Question: A compound, PQ2 has the following arrangement of electrons :
The elements P and Q are respectively
a. N, Cl
b. Cl, S
c. O, F
d. Na, F
Question: A sample of pure water, irrespective of its source contains 11.1% hydrogen and 88.9% oxygen. The data supports
a. law of constant proportions
b. law of conservation of mass
c. law of reciprocal proportions
d. law of multiple proportions.
Question: Match the columns by choosing the correct option.
Column I Column II
a. 52 g of He (i) 2 moles
b. 8 g of O2 (ii) 1 mole
c. 2 g of H2 (iii) 0.25 mole
d. 56 g of N2 (iv) 13 moles
a. a.-(i), b.-(iv), c.-(iii), d.-(ii)
b. a.-(iii), b.-(ii), c.-(i), d.-(iv)
c. a.-(iv), b.-(iii), c.-(ii), d.-(i)
d. a.-(iii), b.-(i), c.-(iv), d.-(ii)
Question: If three gases X, Y and Z are arranged in increasing order of their relative molecular mass and the mass of each gas is 10 g at S.T.P
state, which gas will contain the least number of molecules and which will contain the most?
a. X least and Y maximum
b. X maximum and Z least
c. Y maximum and Z least
d. Y least and Z maximum
Question: Which of the following pair of elements represents a mole ratio of 1 : 1?
a. 10 g of calcium and 12 g of magnesium
b. 12 g of magnesium and 6 g of carbon
c. 12 g of carbon and 20 g of calcium
d. 20 g of sodium and 20 g of calcium
Question: How many atoms in total are present in CoCl3.6H2O?
Question: Which of the following has the smallest mass?
a. 4 g of He
b. 6.022 × 1023 atoms of He
c. 1 atom of He
d. 1 mole atoms of He
Question: Which of the following would weigh the highest?
a. 0.2 mole of sucrose (C12H22O11)
b. 2 moles of CO2
c. 2 moles of CaCO3
d. 10 moles of H2O
Question: Which of the following molecules are diatomic?
(i) Nitrogen (ii) Neon (iii) Oxygen
(iv) Sulphur (v) Phosphorus (vi) Ozone
(vii) Fluorine (viii)Hydrogen (ix) Fullerene
a. (ii), (iv), (v) and (vi)
b. (iv), (v) and (ix)
c. (ii) and (vi)
d. (i), (iii), (vii) and (viii)
Question: Match the columns by choosing the correct option.
Column I Column II
(Molecule) (Mass ratio of elements)
a. Water (H : O) (i) 14 : 3
b. Ammonia (N : H) (ii) 1 : 8
c. Carbon dioxide (C : O) (iii) 1 : 1
d. Sulphur dioxide (S : O) (iv) 3 : 8
a. a. – (ii), b. – (i), c. – (iv), d. – (iii)
b. a. – (iii), b. – (ii), c. – (i), d. – (iv)
c. a. – (i), b. – (iv), c. – (iii), d. – (ii)
d. a. – (iv), b. – (iii), c. – (ii), d. – (i)
Question: Arrange the following in the order of increasing mass. (Atomic mass of O = 16 u, Cu = 63 u, N = 14 u)
I. one atom of oxygen
II. one atom of nitrogen
III. 1 × 10–10 mole of oxygen gas
IV. 1 × 10–10 mole of copper
a. II < I < III < IV b. I < II < III < IV
c. III < II < IV < I d. IV < II < III < I
Question. The mass of a single atom of an element X is 2.65X 10-23g. The atomic mass and name of the element is:
a. 16u, oxygen
b. 16u, Sulphur
c. 32u, oxygen
d. 32u, Sulphur
Question. Identify the correct symbol of gold:
Question. 18g of water is electrolysed. The weight of oxygen obtained is:
Question. The balancing of chemical equations is in accordance with:
a. Law of combining volumes
b. Law of constant proportions
c. Law of conservation of mass
d. Both b and c
Question. Molecular weight of CuSO4.5H2O is equal to:
c. 159.5 X90
d. 159.5 +10 + 16
Question. How many moles of electrons weigh 1 kg. Mass of an electron is 9.1X10-31
Question. Which of the following is a correct statement:
a. Na2S is sodium sulphide, Na2SO3 is sodium sulphite, Na2SO4 is sodium sulphate
b. Na2S is sodium sulphite, Na2SO3 is sodium sulphide, Na2SO4 is sodium sulphate
c. Na2S is sodium sulphide, Na2SO3 is sodium sulphate, Na2SO4 is sodium sulphite
d. Na2S is sodium sulphite, Na2SO3 is sodium sulphite, Na2SO4 is sodium sulphide
Question. The formula of Calcium phosphate is:
Question. Arrange the following in increasing number of molecules:
i. 0.5moles of H2
ii. 4g of H2
iii. 18g of H2O
iv. 2.2g of CO2
a. I <iii<iv< ii
b. Iv< i<iii<ii
a. 24g of Mg: 1 mole
b. 35.5g of Cl2: _________
ii. 1 mol
iv. 2.5 moles
Question. Out of 1 g of oxygen gas, 1 g of oxygen atoms and 1g of ozone , maximum number of atoms are present in:
a. 1g of oxygen gas
b. 1g of oxygen atoms
c. 1 g of ozone
d. All have equal number of atoms
Question. The number of atoms present in 0.5 moles of Nitrogen atoms is same as in:
a. 12 g of C
b. 24 g of Mg
c. 8 g of O
d. 32 g of S
Question. Which of the following is not a postulate of Dalton’s atomic theory:
a. All matter is made up of atoms
b. Atoms are tiny indivisible and indestructive ultimate particles
c. Atoms combine in small whole number ratios to form compounds
d. Atoms of different elements can have the same mass
Question. Which is not represented by 1mole of Nitrogen gas?
a. 6.023X1023 molecules of N2
b. 12.046 X1023 atoms of N2
c. 6.023X1023 atoms of N2
d. 28g of N2
Question. 16g of S8 contains:
a. 6.023×1023 Atoms of S
b. 6.023×1023/8 atoms of s
c. 6.023×1023/2 atoms of S
d. 6.023×1023/16 atoms of S
Question. Which of the following has the smallest number of molecules?
a. 0.1 moles of CO2
b. 2g of H2 at STP
c. 16g of O2 gas
d. 3.4g of NH3
Question. An element X has valency equal to 3. What will be its formula with carbonate ions?
Question. The combining capacity of an element is called
c. Atomic number
d. Valence electrons
Case Based MCQs
The knowledge of valencies of various radicals helps us to write the formulae of chemical compounds. The total positive charge on positive ions (cations) is equal to the total negative charge on negative ions (anions) in a molecule.
Therefore, in writing the formula of a compound,the positive and negative ions are adjusted in such a way that the total number of positive charges of positive ions (cations) becomes equal to the total number of negative charges of negative ions (anions).
There is another simple method for writing the formulae of ionic compounds. In this method, the valencies (or positive or negative charges) of the ions can be ‘crossed over’ to give subscripts. The purpose of crossing over of charges is to find the number of ions required to equalise the number of positive and negative charges.
Question: The formula of the sulphate of an element X is X2(SO4)3. The formula of nitride of element X will be
Question: Element X has two valencies 5 and 3 and Y has valency 2. The elements X and Y are most likely to be respectively
a. copper and sulphur
b. sulphur and iron
c. phosphorus and fluorine
d. nitrogen and iron.
Question: The formula of a compound is X3Y. Thevalencies of elements X and Y will be respectively
a. 1 and 3
b. 3 and 1
c. 2 and 3
d. 3 and 2
A mole of an atom is a collection of atoms whose total mass is the number of grams equal to the atomic mass. Since equal number of moles of different elements contain an equal number of atoms it becomes convenient to express the amounts of the elements in terms of moles. A mole represents a definite number of particles viz, atoms, molecules, ions or electrons. This
definite number is called Avogadro number or Avogadro constant which is equal to 6.022 × 1023. Hence a mole represents 6.022 × 1023
particles of the substance. One mole of substance represents one gram-formula of the substance.
One mole of a gas at standard temperature and pressure occupies 22.4 litres.
Question: What is the mass in grams of a single atom of chlorine? (Atomic mass of chlorine = 35.5)
a. 6.54 × 1023 g
b. 5.9 × 10–23 g
c. 0.0025 g
d. 35.5 g
Question: What is the mass in grams of 2.42 mol of zinc? (Atomic mass of Zn = 65.41)
a. 200 g
b. 25 g
c. 85 g
d. 158 g D
Question: How many grams of sodium must be taken to get 1 mole of the element ?
a. 23 g
b. 35.5 g
c. 63.5 g
d. 46 g
Question: How many number of moles are there in 5.75 g of sodium ?
(Atomic mass of sodium = 23)
The molecular mass of a substance is the relative mass of its molecule as compared with the mass of a carbon–12 atom taken as 12 units. The molecular mass of a substance indicates the number of times one molecule of a substance is heavier than 1/12 of C-12 atom. It is equal to the sum of atomic masses of all the atoms present in a molecule. Depending on the number of atoms of same or different elements present in the molecule, it can be monoatomic, diatomic, triatomic, tetratomic or a olyatomic molecule.
Question: Which is an example of a polyatomic molecule?
d. All of these
Question: Carbon dioxide, hydrogen sulphide, calcium chloride and sodium oxide are examples of
a. triatomic molecules
b. triatomic and tetratomic molecules
c. diatomic and triatomic molecules
d. tetratomic molecules.
Question: Total number of atoms in 44 g of CO2 is
a. 6.02 × 1023
b. 6.02 × 1024
c. 1.806 × 1024
d. 18.06 × 1022
According to Dalton’s atomic theory, all matter whether an element, a compound or a mixture is composed of small particles called atoms which can neither be created nor destroyed during a chemical reaction. Dalton’s theory provides a simple explanation for the laws of chemical combination. He used his theory to explain law of conservation of masses, law of constant
proportions and law of multiple proportions, based on various postulates of the theory. Dalton was the first scientist to use the symbols for the elements in a very specific sense. When he used a symbol for an element he also meant a definite quantity of that element, that is one atom of that element.
Question: Which postulate of Dalton’s atomic theory explains law of definite proportions?
a. Atoms of an element do not change during a chemical reaction.
b. An element consists of atoms having fixed mass and the number and kind of atoms in a given compound is fixed.
c.Different elements have different kind of atoms.
d. Atoms are of various kinds.
Question: “If 100 g of calcium carbonate (whether in the form of marble or chalk) is decomposed,56 g of calcium oxide and 44 g of carbon dioxide are formed.” Which law of chemical combination is illustrated by this statement?
a. Law of constant proportions
b. Law of conservation of mass
c. Law of multiple proportions
d. Law of conservation of energy
Question: Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
a. Atoms can neither be created nor destroyed.
b. Each element is composed of extremely small particles called atoms.
c. All the atoms of a given element are identical.
d. During chemical combination, atoms of different elements combine in simple ratios.
Question: When 5 g calcium is burnt in 2 g oxygen,7 g of calcium oxide is produced. When 5 g of calcium is burnt in 20 g of oxygen, then also 7 g of calcium oxide is produced. Which law f chemical combination is being followed?
a. Law of conservation of mass
b. Law of multiple proportions
c. Law of constant proportions
d. No law is being followed.
Assertion & Reasoning Based Mcqs
a. Both assertion and reason are true, and reason is correct explanation of the assertion.
b. Both assertion and reason are true, but reason is not the correct explanation of the assertion.
c. Assertion is true, but reason is false.
d. Assertion is false, but reason is true.
Question: Assertion : The molecular mass and formula unit mass of a substance is the sum of atomic masses of all the atoms in the molecular formula
or formula unit of a compound respectively.
Reason : The only difference between the molecular mass and formula unit mass is that,former is for molecular compounds (covalentcompounds) and latter is for ionic compounds.
However, their numerical value is the same.
Question: Assertion : Both 44 g CO2 and 16 g CH4 have same number of carbon atoms.
Reason : Both contain 1 g atom of carbon which contains 6.023 × 1023 carbon atoms.
Question: Assertion : When 10 g of CaCO3 is decomposed, 5.6 g of residue is left and 4.4 g of CO2 escapes.
Reason : Law of conservation of mass is followed.
Question: Assertion : 1 amu equals to 1.66 × 10–24 g.
Reason : 1.66 × 10–24 g equals to 1/12 th of mass of a C–12 atom.
Question: Assertion : Pure water obtained from different sources such as river, well, spring,sea etc. always contains hydrogen and oxygen combined in the ratio of 1 : 8 by mass.
Reason : A chemical compound always contains same elements combined in same fixed proportion by mass.
Question: Assertion : Law of conservation of mass holds good for nuclear reactions.
Reason : It states that mass can neither be created nor destroyed in a chemical reaction.
Question: Assertion : Molecular weight of SO2 is double to that of O2.
Reason : One mole of SO2 contains double the number of molecules present in one mole of O2.
Question: Assertion : One atomic mass unit (amu) is mass of an atom equal to exactly one-twelfth the mass of a carbon–12 atom.
Reason : Carbon–12 isotope was selected as standard.
Question: Assertion : Atomic mass of aluminium is 27.
Reason : An atom of aluminium is 27 times heavier than 1/12th of the mass of carbon-12 atom. A