Q. At STP, the order of root mean square velocities of molecules of $H_{2},\ N_{2},\ O_{2}\$and $HBr$ is
A) $H_{2} > N_{2} > O_{2} > HBr$
B) $HBr > O_{2} > N_{2} > H_{2}$
C) $HBr > H_{2} > O_{2} > N_{2}$
D) $N_{2} > O_{2} > H_{2} > HBr$
Explanation
(a)
We know that,
$V_{rms} = \sqrt{\frac{3RT}{M}}$
So, as the molecular mass increases, rms speed decreases. Thus, the correct order of root mean square speed is
$H_{2} > N_{2} > O_{2} > HBr$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.