To increase the acidity of the soil for plants that require acidic conditions, you would need to add a compound that produces hydrogen ions (H+) when dissolved in water. Here are the correct options:
1. Iron(II) sulfate (FeSO4): This compound can be added to the soil to increase acidity. When dissolved in water, it dissociates into Fe2+ and SO4^2- ions. The sulfuric acid formed subsequently releases H+ ions into the soil.
FeSO4 (s) → Fe2+ (aq) + SO4^2- (aq)
2. Sodium sulfate (Na2SO4): Sodium sulfate does not increase soil acidity. When it dissolves in water, it forms Na+ and SO4^2- ions but does not contribute hydrogen ions.
3. Aluminum sulfate (Al2(SO4)3): This compound also increases soil acidity. It dissociates into Al3+ and SO4^2- ions, leading to the release of H+ ions.
Al2(SO4)3 (s) → 2Al3+ (aq) + 3SO4^2- (aq)
4. Iron(III) sulfate (Fe2(SO4)3): Similar to iron(II) sulfate, iron(III) sulfate can increase acidity when added to the soil. Upon dissolution, it forms Fe3+ and SO4^2- ions, which contribute to the release of H+ ions.
Fe2(SO4)3 (s) → 2Fe3+ (aq) + 3SO4^2- (aq)
5. Caesium sulfate (Cs2SO4): Caesium sulfate does not increase the acidity of soil. It dissociates into Cs+ and SO4^2- ions, but does not contribute hydrogen ions.
For the purposes of increasing soil acidity, options 1 (iron(II) sulfate), 3 (aluminum sulfate), and 4 (iron(III) sulfate) are suitable choices.