The root mean square velocity of gas molecules at `27^(@)C` is `1365ms^(-1)` .The gas is

Options

A. `O_(2)`
B. `He`
C. `N_(2)`
D. `CO_(2)`

Answer

B

Explanation

Given that , `T=27^(@)C=300K,v_("rms")=1365ms^(-1)`
we Know that , `"rms"=sqrt((3RT)/(M))`
`"or " v^(2)"rms"=(3RT)/(M)`
`"or "M+(3RT)/(v^(2)"rms")=(3xx8.31xx300)/(1365xx1365)kg`
`=(3xx8.31xx300)/(1365xx1365)xx1000g~~4g`
The molecular weight of helium is 4 .