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.

$N{H_3}$

$Bi{H_3}$

$As{H_3}$

$P{H_3}$

${H_2}Se < {H_2}Te < {H_2}PO < {H_2}O < {H_2}S$

${H_2}S < {H_2}O < {H_2}Se < {H_2}Te < {H_2}PO$

${H_2}O < {H_2}S < {H_2}Se < {H_2}Te < {H_2}PO$

${H_2}PO < {H_2}Te < {H_2}Se < {H_2}S < {H_2}O$

Much lesser than ${\rm{N}}{{\rm{H}}_3}$

Equal to that in ${\rm{N}}{{\rm{H}}_3}$

Much greater than in${\rm{N}}{{\rm{H}}_3}$

Slightly more than in ${\rm{N}}{{\rm{H}}_3}$

$N{H_3}$

$Bi{H_3}$

$As{H_3}$

$P{H_3}$

$A{S_2}{O_5}$

${P_2}{O_5}$

${N_2}{O_5}$

$S{b_2}{O_5}$

Much lesser than ${\rm{N}}{{\rm{H}}_3}$

Equal to that in ${\rm{N}}{{\rm{H}}_3}$

Much greater than in${\rm{N}}{{\rm{H}}_3}$

Slightly more than in ${\rm{N}}{{\rm{H}}_3}$

$N{H_3} > P{H_3} > AS{H_3} > Sb{H_3}$

$Sb{H_3} > AS{H_3} > P{H_3} > N{H_3}$

$Sb{H_3} > P{H_3} > AS{H_3} > N{H_3}$

$N{H_3} > Sb{H_3} > P{H_3} > AS{H_3}$