What is the normality of a 1.25 M solution of H2SO4?

Sulfuric acid H2SO4 will give away 2 protons H+ for this reason its normality is 2 times its molarity.

so for H2SO4 M = 2N

For HCl M= 1N because HCl has only one proton H+

H3PO4 for example has 3N = M

so for your case, 6M = 2N and N= 6/2 = 3.