Thank you for reporting, we will resolve it shortly
Q.
The $SrO$ has $NaCl$ structure. If the lattice constant $a =0.514\, nm$ and ionic radius of $Sr ^{2+}=0.113\, nm$. The radius of $O ^{2-}$ ion is :-
Solution:
$2 r _{ Sr ^{+}}+2 r _{ O ^{-2}}=0.514$ nm
$\therefore r _{ O ^{-2}}=0.144$ nm
$=1.44 \times 10^{-10} \,m$