Q.

If radius of second Bohr orbit of the He+ ion is 105.8 pm, what is the radius of third Bohr orbit of Li2+ ion               [2022]

1 158.7 pm  
2 15.87 pm  
3 1.587 pm  
4 158.7 Å  

Ans.

(1)

Radius =r0×n2Z

For He+,n=2,Z=2

rHe+=r0×2×22  ;  105.8=r0×2

r0=105.82pm

For Li2+ ;n=3,Z=3

rLi2+=r0×(3)23=105.82×3=158.7 pm or 1.587 Å