CBSE 2025, Set 2

Question

**Assertion (A):** Cu cannot liberate H$_2$ on reaction with dilute mineral acids.

**Reason (R):** Cu has positive electrode potential. A). Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). B). Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). C). Assertion (A) is true, but Reason (R) is false. D). Assertion (A) is false, but Reason (R) is true.

Edvaya · Accepted Answer

The correct answer is Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).. **A is TRUE:** Copper does not react with dilute mineral acids (like HCl or H₂SO₄) to liberate hydrogen gas. **R is TRUE and correctly explains A:** Cu has a **positive standard electrode potential** ($E°_{Cu^{2+}/Cu} = +0.34$ V), which is greater than that of H⁺/H₂ ($E° = 0.00$ V). This means Cu cannot reduce H⁺ ions to H₂ — the reaction is thermodynamically unfavourable. Only metals with more negative electrode potential than H⁺/H₂ can displace hydrogen from dilute acids. **Answer: (A) — Both true, R correctly explains A.**

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