Off the top of my head i can only answer the 4th question.
Propanone is CH3C=OCH3
If you add HCN to this you get CH3COH(CN)CH3
Addding the acid (with water) converts the CN to a COOH group.
CH3COH(COOH)CH3
There are explanation to these but you don't really need to know them for A-level chem (though you may need to know the mechanism for the first one). You simply have to sit down and learn the reactions, reagents and conditions.