Organic Chemistry

The mechanism of Grignard reaction is given below.

Image from Grignard reaction

Since the reactant is formaldehyde (methanal) and the Grignard reagent is methyl magnesium iodide (with $\ce{I}$ replacing $\ce{Br}$ ), then $\ce{R = CH3}$ and the reaction is:

$\ce{HCHO + CH3 Mg I -> -> -> CH3CHOH}$

The end product of the reaction is $\boxed{\text{ethyl alcohol}}$ (ethanol).

$CH_3MgI + HCHO \rightarrow CH_3CH_2O^- + Mg^{2+} + I^-$

$CH_3CH_2O^- + H_2O \rightarrow CH_3CH_2OH + OH^-$

Methyl magnesium iodide becomes ethyl alcohol. Formaldehyde is methanal.

Answer: $\boxed{Ethyl~Alcohol}$