The density of neon will be hi highest at:

According to ideal gas equation,

$d=\frac{PM}{RT}$

$\begin{array}{l}\mathrm{P}=\frac{\mathrm{n}}{\mathrm{V}}\mathrm{RT}=\frac{\mathrm{w}}{\mathrm{mV}}=\mathrm{RT}\\ \mathrm{P}=\frac{\mathrm{dRT}}{\mathrm{m}}\\ \mathrm{d}\propto \frac{\mathrm{P}}{\mathrm{T}}\end{array}$

So, neon has the highest density at $0^{\circ }\mathrm{C},2\mathrm{atm}$