Which of the following gases will have the highest rate of diffusion?

Case $-1:$ An ideal gas of molecular weight $M$ at temperature $T$.
Case $-2:$ Another ideal gas of molecular weight $2M$ at temperature $T/2$.
Identify the correct statement in the context of the above two cases.

The rms velocity of oxygen molecules at $27^{\circ} C$ is around $800 \ m/s$. The rms velocity of methane molecules at $600 \ K$ temperature is around ...... (in $m/s$)

Identify the correct labels of $A$,$B$,and $C$ in the following graph from the options given below.
Root mean square speed $(V_{rms})$; most probable speed $(V_{mp})$; Average speed $(V_{av})$

At what temperature $(^o C)$ will the $rms$ speed of $CO_2$ be equal to the $rms$ speed of $CO$ at $STP$?

At what temperature will the $RMS$ velocity of sulphur dioxide $(SO_2)$ molecules at $400 \ K$ be the same as the most probable velocity of oxygen $(O_2)$ molecules (in $K$)?