Statement-I : Branched alkanes have lower boiling point than their unbranched isomers
Statement-II :  Branched chain alkanes have relatively small surface area, so less london forces operate in molecules

Statement-I is true but Statement-II is false

Statement-I & II are correct, Statement-II is correct explanation of Statement-I

Statement-I is false but Statement-II is true

Statement-I & II are correct, Statement-II is not correct explanation of Statement-I