Explanation

(c) Fundamental frequency of closed pipe
$n = \frac{v}{4l} = 220\ Hz \Rightarrow v = 220 \times 4l$
If $\frac{1}{4}$ of the pipe is filled water then remaining length of air column is $\frac{3l}{4}$
Now fundamental frequency $= \frac{v}{4\left( \frac{3l}{4} \right)} = \frac{v}{3l}$ and
First overtone $= 3 \times$ fundamental frequency
$= \frac{3v}{3l} = \frac{v}{l} = \frac{220 \times 4l}{l} = 880\ Hz$