Final answer:
The cation that could be present is calcium ion (Ca²⁺) because calcium hydroxide precipitates when hydroxide is added, while calcium sulfate remains soluble in water. The correct answer is option: b. Ca²⁺
Step-by-step explanation:
The cation that could be present in a solution that does not form a precipitate with sulfate ions but does with hydroxides is calcium ion (Ca²⁺). This is because calcium sulfate (CaSO₄) is relatively soluble in water and does not easily form a precipitate, whereas calcium hydroxide (Ca(OH)₂) is less soluble and will precipitate when sodium hydroxide is added to a solution containing calcium ions.
The other cations listed, such as Mg²⁺, K+, and Li+, are not consistent with the observations provided, as magnesium also forms a precipitate with hydroxide ions and potassium and lithium do not typically form precipitates with hydroxide ions due to their higher solubility in water.