The first law of therodynamics state that ae = q - w . is this also a statement of the principle of a conservative of energy ?

The first law of thermodynamics is concerned with the conservation of energy. The key concept in this law is that the change in internal energy is equal to the heat that flows into the system minus the work done. This is the same as saying that if we apply heat to the system, the system may store it as internal energy or use it to perform the work.

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.