A radioactive nucleus of mass number A and atomic number Z, emits an alpha particle first and then a beta negative particle. The mass number and atomic number of the daughter nucleus will be

$A-4, Z-1$

The correct answer is Option (1) → $A-4, Z-1$

An alpha (α) particle is a helium nucleus consisting of 2 protons and 2 neutrons. So, when a nucleus emits an alpha particle, its mass number decreases by 4 and its atomic number decreases by 2.

Mass number after α-decay = A - 4

Atomic number after α-decay = Z - 2

A beta minus (β⁻) particle is an electron emitted when a neutron in the nucleus converts into a proton. This increases the atomic number by 1 but the mass number remains unchanged.

Mass number after β⁻-decay = A - 4

Atomic number after β⁻-decay = (Z - 2) + 1 = Z - 1