Consider the acidity of the benzylic hydrogens in I 4-nitrotoluene, II toluene and III 4-methoxytoluene. The correct order of decreasing acidity is:

The acidity depends on the stability of the benzyl anion, with charge at ortho and para carbons. A para nitro group stabilises it by -M and -I, increasing acidity. A para methoxy group is a net donor (+M) towards the anionic centre and destabilises it. So I > II > III.