Q. Difference between nth and (n + 1)th Bohr’s radius of hydrogen atom is equal to (n – 1)th Bohr’s radius. The value of *n* is

(a) 1

(b) 2

(c) 3

(d) 4

**Ans: (d)**

Sol: r_{n} ∝ n^{2}

r_{n+1} ∝ (n+1)^{2}

r_{n-1} ∝ (n-1)^{2}

A/c to question ,

(n+1)^{2} – n^{2} = (n-1)^{2}

2n + 1 = n^{2} – 2n +1

n^{2} – 4n = 0

n(n-4) = 0

n = 4