When an isotope emits an alpha particle, its atomic number
, and its mass number

A is reduced by 2, is reduced by 4
B is reduced by 4 is reduced by 2
C stays the same, is reduced by 4
D is increased by 1, stays the same

The atomic number of the isotope is reduced by 2 and atomic mass is reduced by 4.

Explanation:

Alpha particle is doubly ionized helium atom. The atomic mass of helium atom is 4 u and atomic number of helium atom is 2. The emission of alpha particle means doubly ionized helium atom will be released from the isotope.

Hence, the emission of the alpha particle will decrease the atomic mass by 4 and atomic number by 2.

Hence, option(a) is correct