Ascientific theory
a. describes what occurs every time in a given situation
b. is not validated by experimentation
c. can never be changed
d. is an explanation for a set of events

the answer is D hope this helps :)

The correct answer is option D.

Explanation:

A scientific theory is an in depth explanation of an observed phenomena or an events which are strongly supported by repeated observations and experiments. They can be repeatedly tested and verified by the means of experiments in accordance to scientific methods

Hence, the correct answer is option D.

these nuts

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.