The $RMS$ velocity $(u_{rms})$ of one mole of an ideal gas was measured at different temperatures and the following graph is obtained. What is the slope $(m)$ of the straight line?
($x$-axis $= T$ $(K)$; $y$-axis $= (u_{rms})^2$; $M =$ molar mass; $R =$ gas constant)

• A
  $(\frac{3 R}{M})^{1 / 2}$
• B
  $(\frac{M}{3 R})^{1 / 2}$
• C
  $\frac{M}{3 R}$
• D
  $\frac{3 R}{M}$