(a) Name the radiations that are emitted during the decay of a nucleus, which has highest penetrating power?

(a) Gamma (γ) radiation.

(b) No, the emission of gamma radiation does not result in a change in the mass number as they are a form of electromagnetic radiation, essentially high-energy photons, and they have no mass or charge. Since they are massless, their emission does not affect the number of protons or neutrons in the nucleus, and therefore the mass number remains unchanged.