CBSE Class 10 Science 2017 · Paper 31/1/1 · Question 7

X (${\text{C}}_4{\text{H}}_8$) is most likely to show an addition reaction. Justification: ${\text{C}}_4{\text{H}}_8$ fits the general formula of the alkenes, ${\text{C}}_n{\text{H}}_{2n}$ with $n=4$, so X is most likely an unsaturated hydrocarbon (a butene) with a carbon–carbon double bond across which atoms can add. Y, ${\text{C}}_5{\text{H}}_{12}$, fits ${\text{C}}_n{\text{H}}_{2n+2}$ with $n=5$: it is a saturated alkane (such as pentane) with only single bonds, so it has no double bond to add across and reacts by substitution instead. Equation (addition of hydrogen in the presence of a nickel catalyst): ${\text{CH}}_3-\text{CH}=\text{CH}-{\text{CH}}_3+{\text{H}}_2\stackrel{\text{Ni}}{\to }{\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_3$, that is, ${\text{C}}_4{\text{H}}_8+{\text{H}}_2\stackrel{\text{Ni}}{\to }{\text{C}}_4{\text{H}}_{10}$ (butane).