The following reaction shows the process of rusting. 4fe + 3o2 2fe2o3 this chemical reaction should be classified as

Synthesis reaction

Explanation:

Corrosion is the process of slow eating away of metal due to attack of atmospheric gases on the surface of metal resulting into formation of compounds such as oxides, sulfides , carbonates etc is called as corrosion.

Corrosion of iron is called as rusting. Rust is hydrated ferric oxide .

Synthesis reaction is a chemical reaction in which two reactants are combining to form one product.

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.