Question

In a nuclear decay, after the emission of one $\alpha$-particle and one $\beta$-particle

• A. atomic number remains unchanged
• B. mass number is reduced by 4 units
• C. mass number is reduced by 8 units
• D. mass number increases by 4 units
• E. atomic number is increased by 2 units

Hint:

Emission of an $\alpha$-particle reduces the mass number by 4, while a $\beta$-particle changes only the atomic number.

Answer 1

The Correct Option is B

Step 1: An $\alpha$-particle consists of 2 protons and 2 neutrons, meaning its emission reduces the atomic number by 2 and the mass number by 4. Step 2: A $\beta$-particle is an electron emitted when a neutron decays into a proton, meaning its emission increases the atomic number by 1 but does not change the mass number. 
Step 3: Thus, the net effect of emitting one $\alpha$-particle and one $\beta$-particle is: 
- Mass number decreases by 4 (due to the $\alpha$-particle). 
- Atomic number decreases by 2 (from $\alpha$) but increases by 1 (from $\beta$), leading to a net decrease of 1. 
Step 4: Since the question asks about the mass number, the correct answer is (B).