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Q.
The most stable conformation for $n$-butane is
KVPYKVPY 2010Hydrocarbons
Solution:
The most stable conformation for $n$-butane is the staggered form, where the methyl group and $H$-atoms of one carbon are far apart from the groups of other carbon atom and, hence have minimum repulsion between them. Such, type of conformation is shown in option (a).