a vessel of volume v=5 litre contains 1.4 gm nitrogen and 0.4 gm helium at 1500K. if 30% of the nitrogen molecules are dissociated into atoms then find gas pressure.(assume t constant)

Hi..
First of all calculate the total number of moles of the molecules in the undissociated case for the given amounts of the two gases.
And find the pressure corresponding to them.
Finally, calculate the no. of molecules dissociated and also the total number of undissociated molecules and then calculate the pressure corresponding to that.

Hope this helps you out.
Regards