Students in science class watched as their teacher demonstrated various changes. picture a. shows a strip of magnesium ribbon, a silver metal, in a test tube of hydrochloric acid. bubbles are forming as the metal ribbon disappears. also, the test tube feels warmer. picture b. shows a container of water being heated and bubbles forming as the water bubbles. which picture illustrates a chemical change? explain.

a) picture a. the magnesium ribbon disappears.
b) picture a. gas bubbles are produced and there is a temperature change.
c) picture b. bubbles are being produced as the water is being heated on the burner.
d) picture b. there is a change in temperature as the water begins to boil and bubbles are being produced.

I think the answer is B).

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.

i believe the answer is three water molecules