(N/A) Organometallic compounds: Compounds in which a carbon atom is directly bonded to a metal atom are called 'organometallic' compounds.
$(b)$ Grignard Reagent: Alkyl magnesium halides $(RMgX)$ are formed by the reaction of organic halides with magnesium metal in dry ether. This was discovered by Victor Grignard in $1900$.
$R-X + Mg \xrightarrow{\text{dry ether}} R^{-\delta}-Mg^{+\delta}-X^{-\delta}$
$CH_3CH_2Br + Mg \xrightarrow{\text{dry ether}} CH_3CH_2MgBr$
$(c)$ Reactivity of Grignard Reagent: The $C-Mg$ bond is highly polar due to the electropositive nature of magnesium. The carbon atom carries a partial negative charge $(R^{-\delta})$,making it highly reactive.
It reacts with any source of protons to form hydrocarbons:
$RMgX + H_2O \rightarrow RH + Mg(OH)X$
Grignard reagents react with water,alcohols $(R'OH)$,and amines to yield hydrocarbons,acting as strong nucleophiles.