CBSE Class 10 Science 2017 · Paper 31/1/2 · Question 8

X (${\text{C}}_3{\text{H}}_6$) is the one most likely to show an addition reaction. Justification: ${\text{C}}_3{\text{H}}_6$ fits ${\text{C}}_n{\text{H}}_{2n}$, the general formula of the alkenes, so X is most likely propene, an unsaturated compound with a carbon–carbon double bond, and addition takes place across a double bond. Y, ${\text{C}}_4{\text{H}}_{10}$, fits ${\text{C}}_n{\text{H}}_{2n+2}$: it is an alkane, saturated, with only single bonds, so it cannot add anything. Equation: ${\text{CH}}_3\text{CH}={\text{CH}}_2+{\text{H}}_2\stackrel{\text{Ni catalyst}}{\to }{\text{CH}}_3{\text{CH}}_2{\text{CH}}_3$ (propene and hydrogen give propane).