Which answer below correctly identifies the type of change and the explanation when potassium iodide and lead nitrate are mixed?
a. physical change because the observation of a solid forming is evidence of a state change, which is reversible
b. physical change because even though the mixture had a color that was different from either of the two solids alone, each solid’s physical properties remained exactly the same
c. chemical change because two substances were mixed, which always results in the formation of a new substance
d. chemical change because both a color change and a solid formation were observed, which provide strong evidence of a new substance

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.

the answer your looking for is c).