Which one of the following compound will show addition of HBr to alkene according to markownikoff's rule?

Markovnikov's rule is applicable for the addition of unsymmetrical reagents to unsymmetrical alkenes.

But-2-ene ($CH_3-CH=CH-CH_3$) is a symmetrical alkene.

Hex-3-ene ($CH_3-CH_2-CH=CH-CH_2-CH_3$) is a symmetrical alkene.

Ethene ($CH_2=CH_2$) is a symmetrical alkene.

2-methylpropene ($CH_3-C(CH_3)=CH_2$) is an unsymmetrical alkene.

Therefore, 2-methylpropene will undergo addition of HBr according to Markovnikov's rule.