SI : Crude oil obtained from the field is taken to a refinery for treatment. S6 : Lubricating oils of various grades are obtained last of all. P : The gas th at com es o ff later is condensed into paraffin. Q : This allows substances with different boiling points to be separated. R : The first vapours to rise when cooled provide the finest petrol. S : The commonest form of treatment is heating. The proper sequence should be:
- AS Q R P
- BR S P Q
- CS R P Q
- DR P Q S
Explanation
The proper sequence is S-Q-R-P, option (a). Crude oil goes to the refinery for treatment (S1). The commonest treatment is heating (S). This separates substances with different boiling points (Q). The first vapours, when cooled, provide the finest petrol (R). The gas that comes off later is condensed into paraffin (P), and lubricating oils are obtained last of all (S6).