Q.Normality of 0.3M phosphorus acid (H3PO3) is –

Normality and Equivalent Concept

Normality ($N$) is a concentration unit defined as the number of gram-equivalents of solute dissolved per litre of solution:

It is linked to molarity ($M$) through the n-factor, which is the number of reactive units per formula unit — the basicity for an acid, the acidity for a base, the number of electrons exchanged for a redox species, or the total charge for a salt:

The gram-equivalent mass equals molar mass divided by the n-factor.

Worked example: Phosphorous acid, $H_3PO_3$, is dibasic (only two of its three H atoms are ionisable; the third is bonded directly to phosphorus). Its n-factor is therefore $2$, not $3$. A $0.3\ M$ solution has

$N = 0.3 \times 2 = 0.6\ N.$ …