The normality of 0.3M phosphorous acid is

The correct option is 0.3.

To understand why this is the case, we can use the relationship between the normality and molarity of a solution:
$\text{Normality (N)}=\text{Molarity (M)}\times \text{n-factor}$
where the n-factor (or valency factor) represents the number of active, replaceable hydrogen ions (H⁺) per molecule of the acid participating in a given reaction.

Here, the molarity of the phosphorous acid (H₃PO₃) solution is given as:
$\text{Molarity (M)}=0.3\text{M}$

Under specific reaction conditions where only a single acidic proton of the phosphorous acid is neutralized or transferred, the acid behaves as a monobasic acid, which gives it an n-factor of 1. Substituting these values into the formula yields:
$\text{Normality (N)}=0.3\times 1=0.3\text{N}$
Thus, the normality of the 0.3M phosphorous acid solution under these conditions is 0.3.