Orthophosphoric acid ($H_3PO_4$) is a tribasic acid.

Hypophosphorous acid ($H_3PO_2$) is a tribasic acid.

Pyrophosphoric acid ($H_4P_2O_7$) is a tetrabasic acid.

Phosphorous acid ($H_3PO_3$) is a dibasic acid.

$A{S_2}{O_5}$

${P_2}{O_5}$

${N_2}{O_5}$

$S{b_2}{O_5}$