$\begin {array} {1 1} (1)\;2-Methyl-2,3-diethyl\: pentane & \quad (2)\;4-Ethyl-3,3-dimethyl\: hexane \\ (3)\;3, 4-Diethyl-4-methyl\: pentane & \quad (4)\;3-Ethyl-4, 4-dimethyl \: hexane \end {array}$
