Question

Which of the following statement(s) is/are correct concerning redox properties?

• A. A metal M for which E° for the half reaction $M^{n+}$ + ne^{-}$$\longrightarrowM is very negative will be a good reducing agent
• B. The oxidising power of halogens decrease from chlorine to iodine
• C. The reducing power of hydrogen halides increases from hydrogen chloride to hydrogen iodide
• D. Potassium is a better reductant than lithium

Answer 1

Answer: (A), (B), (C)

A, B, C

Answer 2

Statement (A): A very negative E° for $M^{n+}$ + ne^{-}$$\longrightarrowM implies that M has a strong tendency to get oxidized (M $\longrightarrow$ $M^{n+}$ + ne$^{-}$). A substance that readily gets oxidized is a good reducing agent. Thus, (A) is correct.

Statement (B): Oxidising power of halogens is related to their tendency to gain electrons. This tendency decreases down the group ($F_2 > Cl_2 > Br_2 > I_2$) due to decreasing electronegativity and increasing atomic size. Therefore, oxidising power decreases from chlorine to iodine. Thus, (B) is correct.

Statement (C): Reducing power of hydrogen halides (HX) depends on the ease of oxidation of the halide ion ($X^-$). As atomic size increases down the group ($Cl < Br < I$), the electron cloud of the halide ion becomes more diffuse, making it easier to lose electrons. Thus, the reducing power increases in the order HCl < HBr < HI. Thus, (C) is correct.

Statement (D): The standard reduction potential for $Li^+/Li$ is -3.05 V, while for $K^+/K$ it is -2.92 V. A more negative E° indicates a stronger reducing agent. Lithium is the strongest reducing agent among alkali metals in aqueous solution due to its exceptionally high hydration enthalpy. Therefore, lithium is a better reductant than potassium. Thus, (D) is incorrect.