With the increase in temperature of a gas, the fraction of molecules having velocities within a given range around the most probable velocity, would:

With the increase in temperature of a gas, the fraction of molecules having velocities within a given range around the most probable velocity, would decrease.

The Maxwell Boltzmann Distribution curve shows that the percentage of molecules,

$\frac{1}{\mathrm{N}}\frac{\mathrm{dN}}{\mathrm{du}}=4\pi {\left[\frac{\mathrm{M}}{2\pi \mathrm{RT}}\right]}^{\frac{3}{2}}{\mathrm{u}}^2\exp \left[-\frac{{\mathrm{mu}}^2}{2\mathrm{RT}}\right]$

Fraction of molecule $\propto \frac{m}{\mathrm{T}}$

This means that when the gas's temperature rises, fewer molecules will have velocities.