Question:

An allylide on hydrolysis gives allylene. The alkaline earth metal cation of allylide dissolves in dry ether in the presence of alkyl halide to form a Grignard reagent. The allylide is:

Mg2C3

MnC2

Ce2C3

MgBr2

Grignard reagent is formed by Mg. Mg2C3 produces propylene or allylene on reacting with water. Hence Mg2C3 is the allylide.