Describe the following:
(i) Acetylation                               (ii) Cannizzaro reaction
(iii) Cross aldol condensation      (iv) Decarboxylation

(i) Acetylation      
Acetyl group is introduced in an organic compound.  Reagent is acetyl chloride or acetic anhydride.
Bases such as pyridine and dimethylaniline are used to neutralize acid (HCl or acetic acid).
(ii) Cannizzaro reaction
Aldehydes (not having alpha hydrogen atoms) undergo self oxidation-reduction (disproportionation) reaction. One molecule is oxidized to carboxylic acid and other molecule is reduced to alcohol. Concentrated alkali is the reagent.
(iii) Cross aldol condensation  
Aldol condensation between different carbonyl compounds (aldehdyes and ketones). If both reactants contain alpha hydrogen atom, four different products can be obtained.
(iv) Decarboxylation
Loss of $C{O}_2$ from carboxylic acids to form hydrocarbons. For this, sodium salts of carboxylic acids are heated with soda lime.