Hey Sandeep,
The p- nitrophenol is more acidic than phenol because the deactivating nature of nitro group and after loosing the protons it makes more resonance stabilization as nitro group is having strong deactivating nature so it attracts electrons towards it.
Hope you find it informative!

Hi,

When H+ ion is removed from phenol and nitrophenol , negative charge is generated on the ring. This negative charge delocalizes on the ring which is called phenomenon of resonance.

More the resonance contributer more the stability of anion. In case of p-nitro phenol you get extra resonating structure which stabilizes the negative charge. There for it is more easy for p-nitrophenol to loose H+ than phenol. Hence p- nitrophenol is more acidic.

So correct option will be 2.

Hope you find this understandable.