If the mean of first n natural number is 15, then n =

Given:

Mean of first n natural numbers = 15

$\Rightarrow \frac{1+2+3+\ldots+n}{n}=15$

$\Rightarrow \frac{\frac{n(n+1)}{2}}{n}=15$

$\Rightarrow \frac{n+1}{2}=15$

$\Rightarrow n+1=30$

$\Rightarrow n=29$

Hence, the correct option is (d).