Question

For calcium-42, How many protons,

neutrons and electrons are present,
respectively.
A. 20, 42, 20
B. 20, 22, 20
C. 20, 22, 18
D. 42, 20, 20

Answer 1

B. 20, 22, 20

Step-by-step explanation:

The atomic number (Z) of calcium is 20, that is, it has 20 protons.

The mass number (A) of calcium-42 is 42. The mass number is equal to the sum of protons and neutrons. Then,

p⁺ + n⁰ = 42

n⁰ = 42 - p⁺

n⁰ = 42 - 20

n⁰ = 22

Since calcium is electrically neutral, it has the same number of protons (+) and electrons (-). Then, calcium has 20 electrons.