JEE Main · 2022 · 29 Jul 2022 · Shift 2 · Alcohols Phenols and Ethers

A polyhydric alcohol liberates hydrogen with an active metal, one molecule of ${\mathrm{H}}_2$ arising from every two alcoholic $-\mathrm{OH}$ hydrogens, so ${\mathrm{R}(\mathrm{OH})}_x$ gives $\frac{x}{2}$ moles of ${\mathrm{H}}_2$ per mole of alcohol. The sample supplies $\frac{1.84\times 10^{-3}}{92}=2\times 10^{-5}$ mol of $X$, while the gas collected is $\frac{1.344}{22400}=6\times 10^{-5}$ mol of ${\mathrm{H}}_2$ at STP. The ratio of hydrogen to alcohol is $\frac{6\times 10^{-5}}{2\times 10^{-5}}=3$, and since this equals $\frac{x}{2}$, the number of alcoholic hydrogens is $x=6$. The figure $3$ is only the mole ratio $\frac{x}{2}$, not the count of alcoholic hydrogens the question asks for.