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What is the correct relationship between the pH values of solutions of sodium sulphide (pH₁), sodium sulphide (pH₂), sodium selenide (pH₃), and sodium telluride (pH₄)?

1. pH₁ > pH₂ > pH₃ > pH₄
2. pH₁ > pH₂ ≥ pH₃ > pH₄
3. pH₁ < pH₂ < pH₃ < pH₄
4. pH₁ < pH₂ ≥ pH₃ ≥ pH₄

Correct answer: pH₁ > pH₂ > pH₃ > pH₄

Solution

The basicity of the solutions depends on the strength of the conjugate bases of H₂S, H₂Se, and H₂Te. As we move down the group in the periodic table, the acidic strength of the hydrides increases, making their conjugate bases weaker. Thus, the pH decreases in the order pH₁ > pH₂ > pH₃ > pH₄.

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