Q.

Number of collisions per second of molecules of a gas on the wall of a container per m2 will:

1 Increase if temperature and volume both are doubled.  
2 Increase if temperature and volume both are halved.  
3 Increase if pressure and temperature both are doubled.  
4 Increase if pressure and temperature both are halved.  

Ans.

(2,3)

No. of collisions per unit area∝1time between two collisions×area

nA∝Vrmsdistance b/w walls×A       Vrms∝T               Distance b/w walls×A=volume

So nA∝T1/2V

If both T and V are halved, nA increases.