Question

$X^{2-}$ is isoelectronic with ${}_{10}\text{Ne}$ and $1.6$ $g$ of $X^{2-}$ has $0.1$ mole. Thus, the number of neutrons in $X^{2-}$ is:

Answer 1

$X^{2-}$ is isoelectronic with $Ne$. Thus, electrons in $X^{2-}$ $=$ $10$.
Number of protons ($=$ atomic number ) in $X^{2-}$ $=$ $8$.
Also, mole $=$ $\frac{mass}{atomicmass}$
$0.1$ $=$ $\frac{1.6}{A}$
$\therefore A$ $=$ $16$
Also, neutrons $+$ protons $=$ atomic mass $=$ $16$.
$\therefore$ Neutrons $=$ $16-8$ $=$ $8$.