Question

The number of neutrons present in the element ${}_Z^A\text{X}$ is given by ________.

(a) $\text{A-Z}$
(b) $\text{Z}$
(c) $\text{Z + A}$
(d) $\text{Z - A}$

[1 Mark]

Answer 1

Solution:

The correct answer is option (a): $\text{A-Z}$

[1 Mark]

Symbolic representation of an element is given as ${}_Z^A\text{X}$.

• Z = Atomic number = Number of protons
• A = Mass number = Number of protons + Number of neutrons
• X = Symbol of the element

Hence, number of neutrons = Mass number - Atomic number = $\text{A-Z}$