Curium is produced according to this equation - HSC - SSCE Chemistry - Question 9 - 2016 - Paper 1

To determine what X is in the nuclear reaction equation, we need to balance the atomic numbers and mass numbers on both sides of the equation.

In the given equation: $\text{Mass number: } 239 + A = 242 + 1$ $\text{Atomic number: } 94 + Z = 96 + 0$

From the mass number: $A = 242 - 239 - 1 = 2$

From the atomic number: $Z = 96 - 94 = 2$

This indicates that X is an alpha particle (which consists of 2 protons and 2 neutrons). Therefore, the answer is:

(D) An alpha particle