Question

For any anion $X^{-3}$, the mass number is $14$. If anion has $10$ electrons, then number of neutrons in $X_2$ nucleus.

• A. $10$
• B. $14$
• C. $7$
• D. $5$

Answer 1

The correct option is B $14$

We know that mass number = number of protons + number of neutrons

Given the mass number = 14

⇒ number of protons + number of neutrons = 14

Given the anion has 10 electrons and its symbol = $X^{-3}$

⇒ the $X$ atom gained 3 electrons from some other atom to become as anion the $X^{-3}$

So, the original neutral atom of $X$ contains (10 - 3) = 7 electrons

We know that in a neutral atom, number of protons = number of electrons

⇒ the number of protons in the original neutral atom of $X$ = 7

⇒ the number of neutrons in the original neutral atom of $X$ and the anion $X^{-3}$ is mass number of $X$ - number of protons of $X$ = 14 - 7 = 7 neutrons.

⇒ if each atom of $X$ contains 7 neutrons then $X_2$ contains 7 + 7 = 14 neutrons