Explanation

(d)
According to Markownikoff’s rule the addition of a reagent (HX) to an unsymmetrical alkene takes place in such a way that the negative part of the reagent will be attached to that carbon atom which contains lesser number of H-atom.
$Br$
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$CH_{3} - C = CH_{2} + HBr \rightarrow CH_{3} - C - CH_{3}$
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$CH_{3}$ $CH_{3}$
2-methylpropene