Barry makes a hypothesis that driving with his windows closed will increase his gas mileage. If the gas mileage does not change, what should Barry do
next?
A. Conclude that the gas additive has gone bad
B. Assume that the hypothesis is not useful because it made a wrong
prediction
C. Change the results to show that the hypothesis is correct
D. Repeat the experiment to confirm the result

D. Repeat the experiment to confirm the results

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

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.