(a) Larger hydrocarbon molecules can be broken down into alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise more useful molecules by a process called alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise. To break the molecules down the hydrocarbons from oil are heated to alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise them and the hot vapours (gases) are passed over a heated alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise to make the process alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise, so it is more alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise efficient. Breaking compounds down by heat in this way is an example of a reaction known as a alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise.

(b) There are several types of hydrocarbons formed in this reaction and the products include alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise alkanes with no double bonds and alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise alkenes which have a carbon-carbon double bond.

(c) C_nH_2n+2 is the general formula for the series of molecules known as alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise and
C_nH_2n is the general formula for the series of molecules known as alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise where n is the number of alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise atoms in the alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise.

(d) (i) is an example of an alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise.
(ii) is an example of hydrocarbon called an alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise, which is an alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise molecule because it has a carbon-carbon alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise bond.
(iii) is an example of an alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise.
(iv) is an example of an alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise, a type of hydrocarbon described as a alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise molecule because it has all alkanealkanesalkenealkenescarboncatalystcrackingdecompositiondoubleeconmicallyfastermoleculesaturatedsinglesmallerthermalunsaturatedvaporise carbon-carbon bonds.