Atoms and Molecules Practice Questions
Class 9 · Science · 2697 free MCQs with instant results and detailed explanations.
2697
Total
896
Easy
1323
Medium
478
Hard
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Topics in Atoms and Molecules
Molecule
795
Atom
845
Mole Concept
391
Laws of Chemical Combination
666
Sample Questions from Atoms and Molecules
Here are 10 sample questions. Start a quiz to get randomized questions with scoring.
Q1
Easy
What does the law of conservation of mass state?
A.
Mass can be created or destroyed.
B.
Mass is constant in chemical reactions.
C.
Mass only changes its form.
D.
Mass is always lost in reactions.
Show Answer & Explanation
Correct Answer: B
The law states that matter cannot be created or destroyed in a chemical reaction.
Q2
Easy
Which of the following is an example of a chemical change?
A.
Dissolving sugar in water
B.
Burning wood
C.
Melting ice
D.
Boiling water
Show Answer & Explanation
Correct Answer: B
Burning wood results in a chemical reaction creating new substances (ash, smoke).
Q3
Easy
According to the law of definite proportions, a chemical compound always contains:
A.
Variable proportions of elements
B.
Constant proportions of elements
C.
No elements
D.
Only one type of atom
Show Answer & Explanation
Correct Answer: B
This law states that a given compound always contains the same proportion by mass of its elements.
Q4
Medium
Which of the following statements best describes the law of conservation of mass?
A.
Mass can be created or destroyed in chemical reactions.
B.
The total mass of reactants equals the total mass of products.
C.
Atoms are indivisible and cannot change in a reaction.
D.
Chemical reactions can change the nature of elements.
Show Answer & Explanation
Correct Answer: B
The law of conservation of mass states that in a closed system, the mass before and after a chemical reaction remains constant.
Q5
Medium
If 4 g of hydrogen reacts with 32 g of oxygen, what will be the mass of water produced?
A.
36 g
B.
32 g
C.
28 g
D.
4 g
Show Answer & Explanation
Correct Answer: A
According to the law of conservation of mass, the mass of reactants equals the mass of products. Here, 4 g + 32 g = 36 g of water.
Q6
Medium
What does the law of definite proportions state?
A.
Elements combine in fixed ratios to form compounds.
B.
Mass is neither created nor destroyed.
C.
All atoms of an element are identical.
D.
Reactions occur only in gaseous states.
Show Answer & Explanation
Correct Answer: A
The law of definite proportions states that a given chemical compound always contains its component elements in fixed ratio by mass.
Q7
Medium
Which of the following is an example of a chemical reaction that illustrates the law of conservation of mass?
A.
Dissolving salt in water
B.
Burning wood
C.
Melting ice
D.
Evaporating alcohol
Show Answer & Explanation
Correct Answer: B
Burning wood is a chemical reaction where the mass of the reactants (wood and oxygen) equals the mass of the products (ash, gases).
Q8
Hard
According to the Law of Conservation of Mass, if a chemical reaction takes place in a closed system, what will be true about the mass of the reactants compared to the mass of the products?
A.
The mass of reactants will be greater than products.
B.
The mass of reactants will be equal to the mass of products.
C.
The mass of products will be greater than reactants.
D.
Mass cannot be compared as it changes during the reaction.
Show Answer & Explanation
Correct Answer: B
The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction, so the total mass of the reactants must equal the total mass of the products in a closed system.
Q9
Hard
Which law states that mass is neither created nor destroyed in a chemical reaction?
A.
Law of Conservation of Mass
B.
Law of Definite Proportions
C.
Law of Multiple Proportions
D.
Law of Reciprocal Proportions
Show Answer & Explanation
Correct Answer: A
The Law of Conservation of Mass states that the total mass of reactants equals the total mass of products in a chemical reaction.
Q10
Hard
According to the law of definite proportions, how can a compound be characterized?
A.
By its variable composition
B.
By its fixed composition
C.
By its reaction with acids
D.
By its physical state
Show Answer & Explanation
Correct Answer: B
The law of definite proportions states that a compound always contains the same proportion of elements by mass.
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Atoms and Molecules — Class 9 Science Practice Questions Online
This page contains 2697 practice MCQs for the chapter Atoms and Molecules in Class 9 Science. The questions are organized by difficulty — 896 easy, 1323 medium, 478 hard — so you can choose the right level for your preparation.
Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit. This chapter covers 4 topics, giving you comprehensive coverage of the entire chapter.