Explain the methods of preparing alcohols from carbonyl compounds using Grignard reagents.

(N/A) The reaction of carbonyl compounds $(C=O)$ with Grignard reagents $(RMgX)$ involves a nucleophilic addition to form an intermediate adduct,which upon hydrolysis yields an alcohol.
$(i)$ Formaldehyde $(HCHO)$ reacts with a Grignard reagent to form a primary $(1^{\circ})$ alcohol.
$(ii)$ Other aldehydes $(RCHO)$ react with Grignard reagents to form secondary $(2^{\circ})$ alcohols.
$(iii)$ Ketones $(RCOR')$ react with Grignard reagents to form tertiary $(3^{\circ})$ alcohols.