The $\mathrm{p}{K}_a$ values are: phenol 9.95, 3-nitrophenol 8.36, 4-nitrophenol 7.15. The best explanation of why 4-nitrophenol is more acidic than 3-nitrophenol is that

1. Athe nitro group exerts a stronger $-I$ effect at the meta position than at the para position
2. B4-nitrophenol forms intramolecular hydrogen bonds that release the proton more readily
3. Cthe nitro group at the para position donates electrons by $+R$ effect
4. Din the 4-nitrophenoxide ion the negative charge is delocalised onto the nitro group by resonance, which cannot happen from the meta position