Answer the following: Why is the first ionisation enthalpy of chromium less than that of zinc?…
Answer the following:
(i)[1.0]
Why is the first ionisation enthalpy of chromium less than that of zinc?
(Atomic Number of $\text{Cr} = 24$ and $\text{Zn} = 30$)
(ii)[1.0]
Why does pink colour of aqueous $\text{KMnO}_4$ solution disappear when warmed with oxalic acid solution in acidic medium?
Answer
Answer (i)
AIWritten by AI (gemini) - it can contain mistakes.
The electronic configuration of $\text{Cr}$ ($Z = 24$) is $[\text{Ar}] 3d^5 4s^1$. Loss of the first electron leaves a stable, half-filled $3d^5$ configuration. In contrast, $\text{Zn}$ ($Z = 30$) has the configuration $[\text{Ar}] 3d^{10} 4s^2$, where the first electron must be removed from a completely filled, stable $4s^2$ orbital, and $\text{Zn}$ also has a higher effective nuclear charge ($Z = 30$). Therefore, the first ionisation enthalpy of chromium is less than that of zinc.
Answer (ii)
AIWritten by AI (gemini) - it can contain mistakes.
The pink/purple colour of $\text{KMnO}_4$ is due to the permanganate ion ($\text{MnO}_4^-$). In acidic medium, $\text{MnO}_4^-$ oxidizes oxalic acid to $\text{CO}_2$ and is itself reduced to colourless $\text{Mn}^{2+}$ ions, causing the pink colour to discharge:
$2\text{MnO}_4^- + 5\text{C}_2\text{O}_4^{2-} + 16\text{H}^+ \longrightarrow 2\text{Mn}^{2+} + 10\text{CO}_2\uparrow + 8\text{H}_2\text{O}$
From ISC 2026 Chemistry Paper 1, question 10.