Firstly, we need to answer whether acidity affects solubility or not. And Le Châtelier’s Principle clearly states that pH does affect the solubility of a compound.

ZnS

ZnS is an ionic compound and dissociated into Zn²⁺ and S^2- as shown below

ZnS ⇋ Zn²⁺ + S^2-

Adding an acid to the solution means adding H⁺ ions basically which will lead to

2H⁺ + S^2- ⇋ H₂S

This reaction basically decreases the amount of S2- ions which in turn increases the solubility of ZnS, So,

1. Increases Solubility

MgCO₃

MgCO₃ when dissolved goes through the following reaction

MgCO₃ ⇋ Mg²⁺ + CO₃^2-

Here we know that CO^2-₃ is a base. In water it will react as following

CO₃^2- + H₂O ⇋ HCO₃^– + OH^–

These two reaction will create the following equilibrium

MgCO₃ + H₂O ⇋ Mg²⁺ + HCO₃^– + OH^–

Making the solution more acidic means making the equilibrium towards the right which increases the solubility.

2. Increases solubility.

Ba(OH)₂

Ba(OH)₂ as we know is a soluble base which dissociates as

Ba(OH)2 ⇋ Ba²⁺(aq) + 2OH^–(aq)

By adding acid, according to Le Châtelier’s Principle, the equilibrium will move forwards, increasing the solubility

3. Increases solubility.

Ca₃(PO₄)₂

This is similar to MgCO₃. The equilibrium equation will be given by

Ca₃(PO₄)₂ + H₂O ⇋ Ca²⁺ + HPO^2-₄ + OH^–

On adding hydronium ions i.e acid, we will see increase in solubility here as well.

4. Increases solubility.

NiBr₂

This will have the same result as ZnS

NiBr₂ + H⁺ ⇋ Ni²⁺ + HBr

 5. Increases solubility.

CuI

The same reaction will happen in the compound upon the addition of H⁺ ions.

CuI + H⁺ ⇋ Cu⁺ + HI

And it will result in increased solubility.

 6. Increases solubility.