The number of oxalic acid molecules in 250  cm3 of 0.02 N oxalic acid will be:

Oxalic acid H2C2O4⇌2H++C2O42− the valence factor i.e., basicity of acid is 2 Mol. wt. of H2C2O4=(2×1)+(2×12)+(4×16)=2+24+64=90But  molarity = Normality  Valence factor =0.022=0.01∴ No. of millimoles= molarity × Vol in cm3=0.01×250=2.5No. of moles =2.51000=0.0025∴ No. of oxalic acid molecules=0.0025×6.023×1023=1.5×1021