Question

What happens to the mass number of an element when it emits an $\alpha$-particle

• A. Decrease by $4$
• B. Decrease by $3$
• C. Decrease by $2$
• D. Decrease by $1$

Answer 1

The correct option is A Decrease by $4$

Alpha particles are made of $2$ protons and $2$ neutrons.

This means that they have a charge of $+2$, and a mass of $4$.

So mass is decreased by $4$.