The ion of an element has 3 units positive charge. The mass number of the atom is 27 and the number of neutrons is 14. What is the number of electrons in the ion?

The correct option is B

10

Given, mass number = 27 and number of neutrons = 14
Mass number = Number of protons + Number of neutrons.
$\Rightarrow 27=$ Number of protons + 14

Number of protons $=27-14=13$

Now, we know that for a neutral atom,
Number of protons = Number of electrons
Given, that the ion has 3 units positive charge i.e. number of electrons is three less than the number of protons.

So, the number of electrons in the given element $=13-3$
$=10$