Question

Which one of the following will have greatest average speed of its molecules ?
A. 0.5 mol of `O_(2)` at 500 K
B. 0.2 mol of `CO_(2)` at 400 K
C. 1.0 mol of He at 200 K
D. 0.4 mol of `NH_(3)` at 300 K

Answer 1

Correct Answer - C
Average speed `=sqrt((8RT)/(piM))`. Thus, greater the value of `sqrt((T)/(M))`, greater is the average speed. These values are :
`O_(2)=sqrt((500)/(2))=3.95, CO_(2)=sqrt((400)/(44))=3.0`
`He=sqrt((200)/(4))=7.0, NH_(3)=sqrt((300)/(17))=4.2`
Thus, He at 200 K will have highest average speed.