which of the following will be more soluble in an acidic solution than in pure water
The salts that will be more soluble in an acidic solution than in pure water will be those that contain basic anions
Be(OH)2 andSrSO4 are all insoluble or slightly soluble in water, but highly soluble in acid. This is due to the H+ reacting with the anion in some way.
KClO4 is insoluble still because the H+ cannot react with ClO4- to produce the strong acid, HClO4.
CuCN (s) <=> Cu+2 (aq) & CN- (aq)
adding H+ removes the CN-, converting it into the weak acid HCN,
upon which CuCN (s) shifts to the right =>
in an attempt to restore the lost CN- ions
AgCl is soluble only by complexation specifically with HCl. I’m not sure if it’ll complex (and thus lower solubility) with acids like CH3COOH and H2SO4. But your question didn’t ask specifically for the acid, HCl, so I’ll leave it out of the list.