$\frac{\mathrm{v}_{\mathrm{gas}}}{\mathrm{v}_{\mathrm{air}}}=\sqrt{\frac{\rho_{\mathrm{air}}}{\rho_{\mathrm{gas}}}}$
$\Rightarrow \frac{\mathrm{v}_{\mathrm{gas}}}{300}=\frac{1}{\sqrt{2}}$
$\Rightarrow \mathrm{v}_{\mathrm{gas}}=\frac{300}{\sqrt{2}}$
$\therefore \mathrm{v}_{\mathrm{grs}}=150 \sqrt{2}$
Now $\mathrm{n}_{2}-\mathrm{n}_{1}=\frac{\mathrm{v}_{\mathrm{gss}}}{2 \ell}=\frac{150 \sqrt{2}}{2(1)}=75 \sqrt{2}$
$\Rightarrow \Delta \mathrm{n}=106.06 \mathrm{Hz}$
$I.$ The speed of the wave is $4n \times ab$
$II.$ The medium at $a$ will be in the same phase as $d$ after $\frac{4}{{3n}}s$
$III.$ The phase difference between $b$ and $e$ is $\frac{{3\pi }}{2}$
Which of these statements are correct