Correct Answer - A
Structure of `H_(3) PO_(3) (H-overset(O)overset(||)underset(OH)underset(|)(P)-OH)` shows that only two `H` atoms are bonded to the hightly electronegative `O` atom. Thus, it is a dibasic (diprotic) acid,n i.e., it can furnish only two `H` atoms per molecule as `H^(+)` ions in aqueous solution. Its `n` factor is thus, 2 and
`N = 2M = 2(0.3) = 0.6`
