On heating, phosphorous acid disproportionates: 4H3PO3 -> 3H3PO4 + PH3. If 2.0 mol of H3PO3 is heated completely, the number of moles of NaOH needed to neutralise the H3PO4 formed completely is

JEE Advanced levelSingle correct optionDifficulty 3 of 3pn104

On heating, phosphorous acid disproportionates: $4 H X_{3} PO X_{3} 3 H X_{3} PO X_{4} + PH X_{3}$ . If 2.0 mol of $H X_{3} PO X_{3}$ is heated completely, the number of moles of NaOH needed to neutralise the $H X_{3} PO X_{4}$ formed completely is

From the equation 2.0 mol

H X_{3} PO X_{3}

gives

2.0 \times 3/4 = 1.5

mol

H X_{3} PO X_{4}

H X_{3} PO X_{4}

is tribasic, so NaOH needed =

1.5 \times 3 = 4.5

mol.

PH X_{3}

is neutral and consumes none.