Asolution contains some or all of the ions cu2+, al3+, k+, ca2+, ba2+, pb2+, and nh4+. the following tests were performed, in order, on the solution. addition of 6 m hcl produced no reaction. addition of h2s with 0.2 m hcl produced a black solid. addition of (nh4)2s produced a white solid. addition of (nh4)2hpo4 in nh3 produced no reaction. the final supernatant when heated produced a purple flame. identify which of these ions were present in the solution, which were absent, and for which ones no conclusions can be drawn.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

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.