Difference between n^th and (n + 1)^th Bohr’s radius of H-atom is equal to its (n – 1)^th Bohr’s radius. The value of n is:
a) 1
b) 2
c) 3
d) 4

Answer: d
Explanation: r_n ∞ n²
But r_n + 1 – r_n = r_n – 1
(n + 1)² – n² = (n – 1)²
n = 4