I am assuming that the compounds given are Pentane, 3-methyl-hexane, and 2, 4-dimethylpentane considering that the compounds were not separated by a comma.
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Pentane is in the form of a straight chain alkane. This is important as there are many isomers of Pentane, taking different shapes. By it's name it consists of 5 carbon atoms, and the number of hydrogen atoms should be 12, as the compound is nonpolar.
3-methylhexane is an alkane present in a hexane structure at position 3. There are thus 3 molecules at 3 ends of a hexane structure - H3C, CH3, and CH3
2,4-dimethylpentane is an alkane with respect to the formula [(H3C)2CH]2CH2.
With that information, refer to the three attachments below, for each compound given. They are in order -