Question

Assertion (A): Pure water obtained from different sources such as a river, well, spring, the sea always contains hydrogen and oxygen in the ratio of 1:8 by mass.

Reason (R): The total mass of reactants and products during chemical or physical change is always the same.

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true and R is not correct explanation of A
• C. A is correct and R is incorrect
• D. A is incorrect and R is correct

Answer 1

The correct option is B Both A and R are true and R is not correct explanation of A

Pure water has formula $H_{2}O$ always and has atomic masses constant during chemical reaction.

$H_{2}O=$ ratio of mass of $H:O$

$1\times 2:16$

$1:8$

This illustrates the law of definite proportions. And the total mass of reactants and products during chemical or physical change is always the same.

Both assertion and reason correct statement but reason is not the correct explanation of assertion. The correct explanation is based on the law of constant composition.

Option B is correct.