Calculate the Radius of The $n = 4$ Bohr Orbit In $\mathrm { O } ^ { 7 + }$

Multiple Choice

Calculate the radius of the $n = 4$ Bohr orbit in $\mathrm { O } ^ { 7 + }$ (oxygen with 7 of its 8 electrons removed) . (for hydrogen, $r _ { 1 } = 0.0529 \mathrm {~nm}$ )

A) $85 \mathrm { pm }$
B) $95 \mathrm { pm }$
C) $74 \mathrm { pm }$
D) $106 \mathrm { pm }$