Chemistry Question 70 – NEET-UG 2024

A. For 1 mol of ${\text{H}}_2\text{O}$ to ${\text{O}}_2$: The oxidation half-reaction is ${\text{H}}_2\text{O}\to \frac{1}{2}{\text{O}}_2+2{\text{H}}^{+}+2{\text{e}}^{-}$. This shows that 2 moles of electrons are transferred for 1 mole of ${\text{H}}_2\text{O}$ to produce $\frac{1}{2}$ mole of ${\text{O}}_2$. Thus, $2\text{F}$ are required. (A $\to$ II)

B. For 1 mol of ${\text{MnO}}_4^{-}$ to ${\text{Mn}}^{2+}$: The oxidation state of $\text{Mn}$ in ${\text{MnO}}_4^{-}$ is $+7$, and in ${\text{Mn}}^{2+}$ it is $+2$. The change in oxidation state is $7-2=5$. Thus, 5 moles of electrons are transferred, requiring $5\text{F}$. (B $\to$ IV)

C. For 1.5 mol of $\text{Ca}$ from molten ${\text{CaCl}}_2$: The reduction half-reaction is ${\text{Ca}}^{2+}+2{\text{e}}^{-}\to \text{Ca}$. For 1 mole of $\text{Ca}$, 2 moles of electrons are required. For 1.5 moles of $\text{Ca}$, $1.5\times 2=3$ moles of electrons are required. Thus, $3\text{F}$ are required. (C $\to$ I)

D. For 1 mol of $\text{FeO}$ to ${\text{Fe}}_2{\text{O}}_3$: The oxidation state of $\text{Fe}$ in $\text{FeO}$ is $+2$, and in ${\text{Fe}}_2{\text{O}}_3$ it is $+3$. The change in oxidation state is $3-2=1$ per $\text{Fe}$ atom. For 1 mole of $\text{FeO}$ (containing 1 mole of $\text{Fe}$), 1 mole of electrons is transferred. Thus, $1\text{F}$ is required. (D $\to$ III)