These exam oriented questions are based on the chapter Atoms and Molecules taken from the NCERT Chemistry text book for class 9 students.

1. Why do different kinds of matter show different properties?

Answer: Different kinds of matter show different properties because the atoms and molecules that constitute matter have different properties.

2. Which postulate of John Dalton was found to be wrong in the later days?

Answers: According to John Dalton’s Atomic Theory, atoms are indivisible particles that cannot be created or destroyed by chemical reaction. This was later proved to be wrong.

3. How do we indicate the size of an atom?

Answer: We indicate the size of an atom by its radius.

4. Name any two laws of chemical combination

Answer

Law of conservation of mass
Law of definite proportions

5. Define Lavoisier’s law of chemical combination

Answer: Lavoisier’s law of chemical combination is called the law of conservation of mass. According to this law, the total mass of the products is equal to the total mass of the reactants in a chemical reaction.

6. Who proposed the law of constant proportions?

Answer: The law of constant proportions was proposed by Proust in 1779.

7. Hydrogen and oxygen combine in the ratio of 1:8 by mass to get water. What mass of hydrogen is required to react completely with 72 g of oxygen to get water?

Answer: We need 1 gram of hydrogen to react completely with 8 gram of oxygen to form water.
Therefore mass of hydrogen required to react completely with 72 gram of oxygen = 1/8 x 72g = 9 gram