If the r. m.s speed of chlorine molecule is $490 \mathrm{~m} / \mathrm{s}$ at $27^{\circ} \mathrm{C}$, the r. m. s speed of argon molecules at the same temperature will be (Atomic mass of argon $=39.9 \mathrm{u}$, molecular mass of chlorine $=70.9 \mathrm{u}$ )