$v=f \lambda$

$=\lambda \text { is constant for an organ pipe }$

$v=\sqrt{\frac{\gamma R T}{M}}$

$v=\frac{1}{\sqrt{M}}$

$v$ is maximum when $M$ is least. Thus, velocity of sound in air is maximum when $M$ is least.

Since $f \propto v$ so $f \propto \frac{1}{\sqrt{M}}$

Hence, frequency is maximum when $M$ is least.

Hence, among options answer is $H _2$.