The solubility product to different sparingly soluble salts are

1) XY = 4 × 10^–20

2) X₂Y = 3.2 × 10^–11

3) XY₃ = 2.7 × 10^–31

The increasing order of solubility is

$\text{ 1) }\mathrm{XY}\left(\mathrm{s}\right)\rightleftharpoons \mathrm{XY}\left(\mathrm{aq}\right)\to \underset{ }{\underset{{\mathrm{S}}_1}{{\mathrm{X}}^{+} }+\underset{{\mathrm{S}}_1}{{\mathrm{Y}}^{-}}}$

K_sp = S₁ x S₁ ⇒ S₁ = 2$\times$10^-10

$\text{ 2) }{\mathrm{X}}_2\mathrm{Y}\left(\mathrm{s}\right)\rightleftharpoons \underset{{\mathrm{S}}_2}{\mathrm{XY}}\left(\mathrm{aq}\right)\to \underset{2{\mathrm{S}}_2}{2{\mathrm{X}}^{+}}\left(\mathrm{aq}\right)+\underset{{\mathrm{S}}_2}{{\mathrm{Y}}^{-2}}\left(\mathrm{aq}\right)$

K_sp = (2S₂)² x S₂ ⇒  3.2 x 10^-11 = 4S₂³

                                     ⇒  S₂ = 2 x 10^-4

$\text{ 3) }{\mathrm{XY}}_3\left(\mathrm{s}\right)\rightleftharpoons \underset{{\mathrm{S}}_3}{{\mathrm{XY}}_3(\mathrm{a}}\mathrm{q})\to \underset{{\mathrm{S}}_3}{{\mathrm{X}}^{+3}}\left(\mathrm{aq}\right)+\underset{3{\mathrm{S}}_3}{3{\mathrm{Y}}^{-}}\left(\mathrm{aq}\right)$

 K_sp = (S₃)² x (3S₃) ⇒  2.7 x 10^-31 = 27S₃⁴

                                     ⇒  S₃ = 10^-8