[DesiNits]

Can bromoethane be converted to deuterated ethane by using NaBD4?

C2H5Br + NaBD4 -> C2H5D

If not, what are other methods to so?

[Babcock_Hall]

Do you know what Grignard reagents are?

[Enthalpy]

Really mono-deuteriated? Users often want deuterium everywhere.

Any chance with D₂ and light? D₂ and heat? LiD maybe (except that people will ask why you plan LiD...)?

[Babcock_Hall]

@OP, I don't think your reaction is likely to succeed, but there is a two-step synthesis that will do the trick.  If you write it out, one of us can critique it.

[DesiNits]

Yes, I perfectly know what Grignard reagents are @Babcock_Hall
I wanted to know more. Thanks.

[billnotgatez]

@DesiNits
If you have not read forum rules already, please do so.
Just dumping answers is not typically done here.
I think you have been given 2 hints that will let you deduce some possible answers and thus learn.

[Babcock_Hall]

Yes, I perfectly know what Grignard reagents are @Babcock_Hall
I wanted to know more. Thanks.

Let's see your proposed route then.