CBSE Class 9 | Science | Atoms and Molecules | Assertion Reasoning Questions (Solved) #eduvictors #class9Chemistry

CBSE Class 9 | Science | Atoms and Molecules | Assertion Reasoning Questions (Solved)

DIRECTION: In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as:

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).

(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).

(c) Assertion (A) is true but reason (R) is false.

(d) Assertion (A) is false but reason (R) is true.

Q1. 

Assertion: When 10 g of CaCO₃ is decomposed, 5.6 g of CaO is left and 4.4 g of CO₂ escapes.

Reason: The law of conservation of mass is followed.

Q2. 

Assertion: Water sourced from various outlets like rivers, wells, springs, seas, etc., consistently comprises hydrogen and oxygen in a mass ratio of 1:8.

Reason: A chemical compound invariably consists of identical elements combined in a constant and fixed mass proportion.

Q3. 

Assertion: The Law of Constant Proportion states that a chemical compound always contains the same elements combined in the same fixed proportion by mass.

Reason: Isotopes of an element may have different masses, leading to variations in the fixed proportion by mass in a chemical compound.

Q4. 

Assertion: 1 unified mass is equal to 1.6 × 10⁻²⁴g

Reason: One unified atomic mass is equal to the one-twelfth (1/12) of the mass of a carbon-12 atom. It is a relative mass unit.

Q5. 

Assertion: The law of conservation of mass holds good for nuclear reaction.

Reason: In nuclear reactions two small atomic nuclei fuse into one nucleus or one large atomic nucleus splits into smaller fragments.

Q6.

Assertion: The atomic mass of aluminium is 27u.

Reason: The average mass of an aluminium atom is 27 times greater than 1/12 of the mass of a carbon-12 atom. 

Q7.

Assertion: In H₂S the valency of S is 2.

Reason: The atomicity of sulphur is 8.

Q8. 

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.

Reason: The molecular mass or formula unit mass of a compound is a useful tool for understanding the composition and properties of matter.

Q9. 

Assertion: Compounds composed of metals and nonmetals contain charged species called ions.

Reason: Metals tend to lose electrons to form positively charged ions (cations), while nonmetals tend to gain electrons to form negatively charged ions (anions).

Q10.

Assertion: The molecular mass of water is 18u

Reason: It is the sum of the total number of atoms present in the given molecule.

Answers: 

1. (a) 

2. (a)

3. (c) Isotopes are variations of an element with different masses due to a different number of neutrons. However, the Law of Constant Proportion is based on the assumption that the elements in a compound are in their standard form, which means isotopic variations are not considered. Therefore, the reason is false in the context of the assertion.

4. (a)

5. (d)

6. (a)

7. (b) Both A and R are true but R is not the true explanation of A.

8. (b)  

9. (a)

10.(c) 

👉See Also:

How to learn naming Chemical Formula
Ch 3 - Atoms and Molecules
Ch 3 - Atoms and Molecules (Worksheet)
Ch3 - Atoms and Molecules (MCQs) 
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Ch 3 - Atoms and Molecules (MCQs-2)
Ch 3 - Atoms and Molecules - Atomicity of Elements (Worksheet)
All about Names of the Chemical Elements
Ch 3 - Atoms and Molecules (Important Definitions)
Ch 3 - Formulae of Simple Compounds
Colour of Compounds/Salts
Ch3 - Atoms and Molecules (Very short Answer-Based Questions) - Solved

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