For an ideal gas, which of the following statements about molecular speeds are correct?

ADoubling the kelvin temperature doubles the rms speed
BAt the same temperature, the most probable speed of $He$ (4) is $22$ times that of $O X_{2}$ (32)
CThe rms speed depends on pressure at constant temperature
DThe rms speed of a gas at $T$ is equal to its most probable speed at $1.5 T$

Answer: B, D

u_{rms} = 3 RT / M

: doubling

T

multiplies it by

2

, not 2 (A wrong).

u_{mp} \propto 1/ M

32/4 = 8 = 22

(B). Speeds depend on

T

and

M

only, not on

P

(C wrong).

3 RT / M = 2 R (1.5 T) / M

(D correct).