Does anyone know the correct drying agent for hydrogen selenide. Please?

I would pass the gas through anhydrous CaCl2. It will not react with that. There are better drying agents, but these are either alkaline, or too strongly oxidizing.

 

You could also give it a try with P4O10, which is very good, but also more expensive and harder to obtain. But I guess, that if you have access to H2Se, that you also will have access to P4O10.

 

Do not use Mg(ClO4)2 or concentrated H2SO4. These certainly are too oxidizing and may lead to destruction of the H2Se.

In the case of Mg(ClO4)2 it might lead to the destruction of the H2Se, the equipment and significant bits of the lab and experimenter.

Silica gel or CaSO4 might work, but there would probably be some absorbtion which would be more than a little troublesome when you came to reuse the drying agent.

In the case of Mg(ClO4)2 it might lead to the destruction of the H2Se, the equipment and significant bits of the lab and experimenter.

LOL

 

I personally, however think that things are not that bad. Perchlorate/reductor mixes actually are quite "stable" and they need a considerable source of heat to be ignited.