Question

A nucleus with atomic number Z and mass number A undergoes alpha decay. Which of the following is true?

• A. increases by 2 and A decreases by 4
• B. decreases by 2 and A decreases by 2
• C. increases by 1 and A do not change
• D. decreases by 2 and A decreases

Answer 1

The Correct Option is D

When a nucleus undergoes alpha decay, it emits an alpha particle. An alpha particle is composed of 2 protons and 2 neutrons, so it has a charge of +2 (due to the 2 protons) and a mass number of 4.
Given this information: 
1. The atomic number Z  will decrease by 2 because 2 protons are lost.
2. The mass number A will decrease by 4 because the total of 2 protons and 2 neutrons are lost. 
So, the correct answer is: D. Z decreases by 2 and A  decreases by 4