a
We have $v=v \lambda$
or $\lambda=\frac{\mathrm{v}}{\mathrm{v}}=\frac{340 \mathrm{m} / \mathrm{s}}{340 \mathrm{Hz}}=1 \mathrm{m}$
First resonating length,
$l_{1}=\frac{\lambda}{4}=\frac{1}{4} \mathrm{m}=25 \mathrm{cm}$
second resonating length,
$l_{2}=\frac{3 \lambda}{4}=\frac{3 \times 1 \mathrm{m}}{4}=75 \mathrm{cm}$
Third resonating length,
$l_{3}=\frac{5 \lambda}{4}=\frac{5 \times 1 \mathrm{m}}{4}=125 \mathrm{cm}$
So third resonance is not possible since the length of the tube is $120 \mathrm{cm}$.
Minimum height of water necessary for resonance $=120-75=45 \mathrm{cm}$