Question

If a nucleus with an atomic number of 18 and a mass number of 39 undergoes beta minus decay, what
is the new atomic and mass number? (1 point)
Answers below:
Atomic number: 19, Mass number, 38

Atomic number; 19, Mass number: 39

Atomic number: 17, Mass number: 38

Atomic number: 17, Mass number: 39

Answer 1

In beta minus decay, a neutron in the nucleus is transformed into a proton, resulting in an increase in the atomic number by 1 while the mass number remains unchanged.

For a nucleus with an atomic number of 18 (which corresponds to argon, Ar) and a mass number of 39:

- Atomic number before decay: 18
- Mass number before decay: 39

After beta minus decay:
- New atomic number = 18 + 1 = 19
- New mass number = 39 (remains the same)

Thus, the new atomic number is 19 and the new mass number is 39.

The correct answer is:
**Atomic number: 19, Mass number: 39**.