Can you use a glass of sheet as a lid on top of fish tank?

Yes, but make sure that the tank has a filter and an aerator (air stone).
 
No. Even though the fish doesn't need air to breathe, the water still needs to have air in it. If you close it off, then you will not get the water filtering as much, and algae will take over.
 
If there are holes for air, then yes.
A solid glass sheet would prevent proper gas exchange from the tank water to the air.
Unless you have a filter or airator.
 
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