Q.Write the IUPAC name of $(\text{CH}_3)_2\text{CHCH}_2\text{CH}(\text{CH}_3)_2$.

IUPAC names identify the longest chain containing the principal group (the multiple bond, for alkenes/alkynes), number it to give that group the lowest locant, and cite substituents alphabetically with their locants, e.g. 2,4-dimethylpentane. Structurally, the three families differ at their functional carbon: alkanes are $sp^3$ (tetrahedral, $109.5°$), alkenes are $sp^2$ at the double bond (trigonal planar, $120°$, one sigma plus one pi bond), and alkynes are $sp$ at the triple bond (linear, $180°$, one sigma plus two pi bonds). Alkenes are usually prepared by eliminating $\text{HX}$ from an alkyl halide (alcoholic KOH) or $\text{H}_2\text{O}$ from an alcohol (conc. $\text{H}_2\text{SO}_4$), favouring the more substituted alkene (Saytzeff's rule); ethyne is made from calcium carbide and water, and higher alkynes by a double dehydrohalogenation of a dihaloalkane.