CUET Preparation Today
Which of the following statements is not correct? |
$Mn^{3+}$ and $Co^{3+}$ are oxidizing agents in aqueous solution $Ti^{2+}$ and $Cr^{2+}$ are reducing agents in aqueous solution Cu liberates hydrogen from acids in its higher oxidation states, Mn forms stable compounds with oxygen and fluorine. |
Cu liberates hydrogen from acids |
The correct answer is Option (3) → Cu liberates hydrogen from acids Mn³⁺ and Co³⁺ are oxidizing agents in aqueous solution: Correct. Both have high positive standard reduction potentials (E° for Mn³⁺/Mn²⁺ ≈ +1.57 V; Co³⁺/Co²⁺ ≈ +1.82 V), making them strong oxidizing agents as they readily accept electrons to form more stable +2 states. Ti²⁺ and Cr²⁺ are reducing agents in aqueous solution: Correct. Both have negative or low reduction potentials for M²⁺/M or tend to oxidize to stable +3 states (e.g., Cr³⁺ is d³, half-filled t₂g in octahedral complexes), acting as strong reducing agents. Cu liberates hydrogen from acids: Incorrect. Copper lies below hydrogen in the electrochemical series (E° for Cu²⁺/Cu = +0.34 V > 0 V for 2H⁺/H₂). It cannot displace H⁺ from dilute/non-oxidizing acids (e.g., HCl, dilute H₂SO₄) to liberate H₂ gas. (It reacts with oxidizing acids like concentrated HNO₃ or H₂SO₄, but not via simple H₂ liberation.) In its higher oxidation states, Mn forms stable compounds with oxygen and fluorine: Correct. Mn reaches +7 in oxides (e.g., Mn₂O₇) and +4 in fluorides (e.g., MnF₄), both stable due to high electronegativity of O and F stabilizing high oxidation states (though O better supports +7 via multiple bonding). |
