Find radius
(A) `1^(st)` Bohr orbit of H-atom
(B) `2^(nd)` shell of `Li^(+2)` ion `(Z=3)`
(C ) `M` shell of `He^(+)` ion `(Z=2)`

Explanation

`r_(n) = 0.529xx(n^(2))/(Z)Å`
(A) `r_(1)=0.529xx(1^(2))/(1)=0.529Å`
(B) `r_(2)=0.529xx(2^(2))/(3)=(4)/(3)(0.529)Å`
(C ) `r_(3)=0.529xx(3^(3))/(2)=(9)/(2)(0.529)Å`