Question

The basicity of $H_{3}P{O}_2$ is ___

Answer 1

Let us look at the structure of the given acid:

As you can see, two of the three Hydrogen atoms are directly attached to the Phosphorus atom. So phosphinic acid (another name) forms only one salt - hyphosphites or $H_{2}P{O}_2^{-}$
Industrially, it is prepared by a two-step method. With a suitable hot aqueous solution of an alkali, white phosphorus$P_4$ produces hyphosphite ions and Phosphine $-P{H}_3$.This is a disproportionation reaction where the elemental white Phosphorus (oxidation state - 0) is oxidized to hypophosphite (+1 oxidation state) and reduced to Phosphine (-3 oxidation state).
$P_4+3O{H}^{-}+3H_{2}O\to 3{\left[H_{2}P{O}_2\right]}^{-}+P{H}_3$
When this hyphosphite salt is treated with a stronger acid, $H_{3}P{O}_2$ is obtained
${\left[H_{2}P{O}_2\right]}^{-}+H^{+}\to H_{3}P{O}_2$
Alternatively, when we oxidize $P{H}_3$ using Iodine water $H_{3}P{O}_2$ is formed:
$P{H}_3+2l_2+2H_{2}O\to H_{3}P{O}_2+4l^{-}+4H^{+}$