Question

$3X{10}^{-3}$ mole $K_{2}C{r}_2{O}_7$ reacts completely $4.5X{10}^{-3}$ mole $X^{n+}$ to give $X{O}_3^{-}$ and $C{r}^{3+}$. The value of n is :

• A. 3
• B. 1
• C. 0
• D. 4

Answer 1

The correct option is B 1

$\frac{3\times {10}^{-3}\text{moles of}{K}_{2}C{r}_2{O}_7}{4.5\times {10}^{-3}\text{moles of}{X}^{n+}}=\frac{2}{3}$

$\therefore 3$ moles of $X^{n+}$ reacts completely with $2$ moles of $K_{2}C{r}_2{O}_7$

$C{r}_2{O}_7^{2-}+14H^{+}+6e^{-}⟶2C{r}^{3+}+7H_{2}O⟶\left(1\right)$

$X^{n+}+3H_{2}O-4e^{-}⟶X{O}_3^{-}+6H^{+}⟶\left(2\right)$

From equation $2$, we can say that $n=1$

Hence the correct option is B.