(solved)Question 2.43 of NCERT Class XI Chemistry Chapter 2

Let $\displaystyle Z = x$

so protons $\displaystyle p = x$

one -ve charge $\displaystyle \implies e = x + 1$

given: $\displaystyle n = e + 11.1\% \text{ of } e $

$\displaystyle \therefore n = 1.111e $

$\displaystyle \implies n =1.111(x + 1)$

but $\displaystyle n + p = A = 37$ (given)

$\displaystyle \therefore 1.111(x + 1) + x = 37$

$\displaystyle \implies x = 17$

$\displaystyle \implies Z = 17 \text{ (chlorine)}$

$\displaystyle \therefore $ ion is $\displaystyle ^{37}_{17}\text{Cl}^-\:\underline{Ans} $