Step 1: Understanding Grignard Reagents
Grignard reagents are organomagnesium compounds of the form \( {R} - {MgX} \). Step 2: Evaluating the Options
They act as strong nucleophiles.
They react with carbonyl compounds to form alcohols.
They are not organomanganese compounds (which contain Mn instead of Mg).
Thus, the correct answer is (D).