4:24 know the general formula for alkenes

Alkenes have the general formula C_nH_2n

So an alkene always has twice as many hydrogen atoms as carbon atoms.

Past paper questions on spec point:

Spec	Q'stion	Ans	MS
4:24	Jan '13 (1), Q 5 c i	Answer	MkS
4:24	Jan '13 (1), Q 5 c ii	Answer	MkS
4:24	Jan '14 (1), Q 6 c	Answer	MkS
4:24	May '13 (1R), Q 5 c i	Answer	MkS
4:24	May '15 (1), Q 5 b i	Answer	MkS
4:24	May '15 (1), Q 5 b ii	Answer	MkS
4:24	May '17 (1), Q 6 c i	Answer	MkS