The RMS speed of gas molecules is given by:
\[
v_{\text{rms}} = \sqrt{\frac{3RT}{M}},
\]
where \( R \) is the gas constant, \( T \) is absolute temperature, and \( M \) is molar mass. Thus, \( v_{\text{rms}} \propto \sqrt{T} \).
Answer: \( \sqrt{T} \).