At home, Helena is cooking with butter and lard. While the fats sit on the counter, she notices that the butter begins to melt, but the lard doesn't. Based on what she knows about fats, which product most likely contains the most hydrogen atoms

Lard contains the most hydrogen atoms

Explanation:

Unlike butter, lard contains more saturated fats, higher monounsaturated fats, and no trans fat (a type of unsaturated fat).

Thus, the presence of more saturated fats allows for more hydrogen atoms to confer heat stability to lard.

So, lard contains more hydrogen atoms

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.