Question

One radioactive isotope of calcium has an atomic mass of 47. How many protons are in this calcium-47 nucleus? A) 17 B) 20 C) 27 D) 47

Answer 1

The correct number of protons 20. If it is calcium, it has to be 20 protons. 27 is the number of neutrons.

Answer 2

Answer: B) 20

Explanation: Atomic number is equal to the number of electrons or the number of protons for a neutral atom.

Mass number is the sum of number of protons and the number of neutrons.

Mass number = Number of protons + Number of neutrons = 47

General representation of an element is given as:
`_Z^A\textrm{X}` where,

Z represents Atomic number

A represents Mass number

X represents the symbol of an element

Calcium has atomic number of 20. For the given isotope of calcium,
`_(20)^(47)\textrm{Ca}`

Thus number of protons = 20.