'3.6 and 3.7 I can recall the general formula and displayed formulae of alkenes

4.       What is the general formula for alkenes?
CnH2n

5.       Describe and explain the trend in boiling point
Boiling point is higher up the homogeneous series because more energy is needed to break the strong covalent bonds.

6.       Explain why there is no such compound as methene

There is only one carbon atom and no other carbon atom to share a double bond with.

7.       How do you quickly identify from the displayed formula that the hydrocarbon is unsaturated?

By looking at the structure there should be at least one carbon carbon double bond.