$Na X_{2} HPO X_{4}$ (molar mass $142 g mo l^{- 1}$ ) reacts with both acids and bases. Select the correct statement(s).

AWith $HCl$ forming $NaH X_{2} PO X_{4}$ , $n = 1$ and equivalent mass $= 142$
BWith excess $HCl$ forming $H X_{3} PO X_{4}$ , $n = 2$ and equivalent mass $= 71$
CWith $NaOH$ forming $Na X_{3} PO X_{4}$ , $n = 1$ and equivalent mass $= 142$
DWith $NaOH$ forming $Na X_{3} PO X_{4}$ , $n = 2$ and equivalent mass $= 71$

Answer: A, B, C

Count the protons gained or lost per formula unit.

HPO X_{4} X^{2 -} + H X^{+} H X_{2} PO X_{4} X^{-}

takes one (

n = 1

, 142); going on to

H X_{3} PO X_{4}

takes two (

n = 2

, 71).

HPO X_{4} X^{2 -} + OH X^{-} PO X_{4} X^{3 -} + H X_{2} O

removes one proton, so

n = 1

and 142; option 4 is wrong.