When ethanoic acid (CH3COOH) ionizes it loses a hydrogen ion and forms the ethanoate ion CH3COO-. Explain why in this structure (Ethanoate acid), the carbon-oxygen bonds are different from either of the carbon-oxygen bonds in ethanoic acid.
(Basically the C goes from being bonded with one O through a single bond and one in a double bond, to both in single bonds, but one of them being negative)

i do not get it   at all

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.