Question

10) Assertion : law of conservation of mass does not hold good in case of nuclear reaction.
Reason : In nuclear reaction some mass is lost in the form of energy.​

Answer 1

The Law of conservation of mass states that mass can be neither created nor destroyed in a chemical reaction.

Law of conservation of mass does not hold good for nuclear reaction. The mass defect is converted into binding energy.

Thus, the assertion and reason is correct...