Chapter 30 - The Nature of the Atom - Problems - Page 872: 8

Radius of ion when it is in the second excited state is r $=$ $1.058\times$$10^-$$^1$$^0m$

Radius of $n^t$$^h$ orbit is $=$ $r_n$$=$ $an^2/Z$ $a=constant=0.529\times10^-$$^1$$^0 m$ $Z=2 $$ , He$ $r^n=[0.529\times10^-$$^1$$^0 \times $ $(2)^2]/2$ $r^n=1.058\times10^-$$^1$$^0m$