Q.

The radius of the 2nd orbit of Li2+ is x. The expected radius of the 3rd orbit of Be3+ is             [2023]

1 1627x  
2 49x  
3 94x  
4 2716x  

Ans.

(4)

R=0.529×n2Z

(rLi2+)n=2=0.529×(2)23=x

(rBe3+)n=3=0.529×(3)24

(rLi2+)n=2(rBe3+)n=3=r0×(2)23r0×(3)24

x(rBe3+)n=3=1627

(rBe3+)n=3=27x16