The compound with highest boiling point is

In option A, n- hexane has linear chain with six number of carbons. 3 2 2 2 2 3 CH CH CH CH CH CH In option B, n- pentane has linear chain with five number of carbons. 3 2 2 2 3 CH CH CH CH CH In option C, 2,2-dimethyl propane has more branched chain. 3 | 3 3 | 3 CH CH C CH CH In option D, 2-methyl butane has more branched chain. | 3 2 3 | 3 H CH C CH CH CH Greater is the number of carbon atoms, greater will be surface area and higher will be boiling point. n- hexane has more linear straight chain than others which leads to high intermolecular forces of attraction.