$6$ Petroleum is a source of many important chemicals.

$($a$)$ Name two industrial processes which must take place to produce alkenes from petroleum.

$($b$)$ Ethene, $C{H}_2=C{H}_2,$ and propene, $C{H}_2=CHC{H}_3,$ can both be converted into polymers.

$($i$)$ What type of polymerisation takes place when ethene forms a polymer?

$1$

$($ii$)$ What is the empirical formula of the polymer formed from ethene?

$[1]$

$($iii$)$ Propene has the structural formula $C{H}_2=CHC{H}_3.$

Draw two repeat units of the polymer made from propene.