As you move down group one of the periodic table, what happens to the atomic radii? they increase, because of the higher number of occupied energy levels. they increase, because of the stronger attraction between electrons and the nucleus. they decrease, because of the weaker effective nuclear charge. they decrease, because of the lower number of protons.

The correct answer is the atomic radius increase because of the higher number of occupied energy levels.  

Atomic radius increases when going down a group. The valence electrons hold the higher levels because of the enhancing quantum number (n). As a consequence, the valence electrons get further away from the nucleus with the increase in n. The electron shielding inhibits these outer electrons from getting fascinated towards the nucleus. Therefore, they are held, and the resulting atomic radius is greater.  

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.