Assertion and Reason Questions for Class 9 Science Chapter 3 Atoms and Molecules

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Assertion and Reason Questions for Class 9 Science Chapter 3 Atoms and Molecules

Direction: In each of the following questions, a statement of Assertion is given followed by a corresponding statement of Reason. Of the statements, mark the correct answer as
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true

Question 1.
Assertion: The number of particles present in one mole of a substance is fixed.
Reason: The mass of one mole of a substance is equal to its relative atomic mass in grams.

Answer Answer: (a)

Question 2.
Assertion: Atoms always combine to form molecule and ions.
Reason: Atoms of most element are not able to exist independently.

Answer Answer: (d)

Question 3.
Assertion: Atomicity of ozone is three while that of oxygen is two.
Reason: Atomicity is the number of atoms constituting a molecule.

Answer Answer: (a)

Question 4.
Assertion : 1 amu equals to 1.66 x 10-24 g.
Reason : 1.66 x 10-24 g equal to 1/12th mass of a C-12 atom.

Answer Answer: (a)

Question 5.
Assertion : On burning magnesium in oxygen, the mass of magnesium oxide formed is equal to the total mass of magnesium and oxygen
Reason : In a chemical substance, the elements are always present in a definite proportion.

Answer Answer: (b)

Question 6.
Assertion : 1 mole of and H2 each O2 occupy 22.4 L at standard temperature and pressure.
Reason : Molar volume for all gases at the standard temperature and pressure has the different values.

Answer Answer: (c)

Question 7.
Assertion : Molecular weight of oxygen is 16.
Reason : Atomic weight of oxygen is 16.

Answer Answer: (d)

Question 8.
Assertion : Atomic mass of aluminium is 14.
Reason : An atom of aluminium is 27 times heavier than 1/12th of the mass of carbon-12 atom.

Answer Answer: (a)

Question 9.
Assertion : The number of moles of He in 52 g of He is 13.
Reason : The number of moles of an atom is the ratio of its given mass to its molar mass.

Answer Answer: (a)

Question 10.
Assertion : The valency of aluminium is 3 and oxygen is 2.
Reason : The chemical formula of aluminium oxide is Al3O2.

Answer Answer: (c)

Question 11.
Assertion : A molecule is the smallest particle of an element or a compound which is capable of free existence.
Reason : The number of atoms present in one molecule of the substance is called its atomicity.

Answer Answer: (b)

Question 12.
Assertion : Protons cannot be transferred from one atom to another.
Reason : Protons are present deep inside the atom in its nucleus.

Answer Answer: (a)

Question 13.
Assertion: Water molecules always contain hydrogen and oxygen in the ratio 1:8.
Reason: Water obeys law of constant proportions irrespective of source and method of preparation.

Answer Answer: (a)

Question 14.
Assertion: Relative atomic mass of the atom of element is the average masses of the
atom as compared to the mass of one carbon-12 atom.
Reason: Carbon-12 isotope is the standard reference for measuring atomic masses.

Answer Answer: (c)

Question 15.
Assertion : A sodium ion has positive charge.
Reason : Sodium ion has more protons than a neutral atom.

Answer Answer: (c)

Question 16.
Assertion : In water, the ratio of mass of hydrogen to the mass of oxygen is always 1:8 whatever the source of water.
Reason : According to law of constant proportion, the elements are always present in definite proportion by mass in a chemical substance.

Answer Answer: (a)

Question 17.
Assertion : Ions are always positively charged.
Reason : Ions are formed by losing or gaining of electrons.

Answer Answer: (d)

Question 18.
Assertion : One mole of SO2 contains double the number of molecules present in one mole of O2
Reason : Molecular weight of SO2 is double to that of O2

Answer Answer: (d)

Question 19.
Assertion : When 12 g of CaCO3 is decomposed, 4.6 g of residue is left and 4.4 g of escapes. Reason : Law of conservation of mass is followed.

Answer Answer: (d)

Question 20.
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 different fixed proportion by mass.

Answer Answer: (c)

Question 21.
Assertion : Law of conservation of mass holds good for all the reactions.
Reason : I states that energy can neither be created nor destroyed in a chemical reaction.

Answer Answer: (a)

Question 22.
Assertion : Atomicity of oxygen is 4.
Reason : 1 mole of an element contains 6.023 x 1023 atoms.

Answer Answer: (d)

Question 23.
Assertion : Atomicity of O3 is 2.
Reason : 1 mole of an element contains 6.023 x 1023 atoms.

Answer Answer: (d)

Question 24.
Assertion : 52g of He contains 13 x 6.023 x 1023 atoms.
Reason : 1 mole of an element contains 6.023 x 1023 atoms.

Answer Answer: (a)

Question 25.
Assertion: Atoms can neither be sub-divided, created nor destroyed.
Reason: This postulate of Dalton’s theory is the result of law of constant proportion.

Answer Answer: (c)

Question 26.
Assertion: Carbonates are polyatomic ions.
Reason: The carbonate ion consists of one carbon atom and three oxygen atoms and carries an overall charge of.

Answer Answer: (a)

Question 27.
Assertion : Number of gram-molecules of SO2Cl2 in 13.5 g of sulphur chloride is 0.1.
Reason : Gram molecular mass is equal to two gram molecule.

Answer Answer: (c)

Question 28.
Assertion : The total number of electrons present in 16 g of methane gas is 6.022 x 1023
Reason : 1 mole of an element contains 6.023 x 1023 atoms.

Answer Answer: (a)

Question 29.
Assertion : All noble gases are monoatomic.
Reason : Noble gases are highly stable and unreactive.

Answer Answer: (a)

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