The table shows four fractions obtained from crude oil.
| Fraction | Approximate boiling range / °C |
|---|---|
| refinery gases | below 40 |
| petrol (gasoline) | 40 to 100 |
| kerosine (paraffin) | 150 to 250 |
| bitumen | above 350 |
Deduce which of the four fractions is collected nearest the top of the fractionating column.
[1]
Explain why bitumen is collected near the bottom of the column while refinery gases leave at the top.
[2]