methyl butane. Don't forget to use capital letters when writing formulae.
... addition reaction; the hydrogen molecule is split, one of its atoms is added to each carbon atom that is initially double bonded, and an alkene becomes an alkane. --- ... known as hydrogenation.
The brackets indicate a repeating unit in a polymer. In this case, it means that the structure within the brackets is repeated multiple times in the polymer chain, which consists of a main chain of -CH2- units with methyl (-CH3) groups attached.