An atom ${}^{23}\mathrm{A}$ has 11 electrons. Find the number of neutrons in it. [Pg. No. 150]

For atom $^{23}\text{A}$:

Mass number = 23

Number of electrons = 11

Since it is a neutral atom:

Number of protons = Number of electrons = 11

Number of neutrons = Mass number – Number of protons

= 23 – 11 = 12

Therefore, the number of neutrons = 12.