The major product of the following reaction is

Step-by-step solution

Grignard reagents are made by adding the haloalkane to small bits of magnesium in a flask containing ether. Grignard reagent is highly reactive compound so, it is used in preparation of many important compounds. When it is reacted with water it gives alkane. In this case it will react with heavy water which will replace Mg with Deuterium.