It is because of the chances of survival. Fish and Frogs lay hundreds of eggs at a time bcoz thr is very less survival chances of frogs' n fishes's eggs whereas a hen lays  just a egg at  the time bcoz the survival chances  of it is veryyyy much more.
Thts the only posssible reason

Hope it helps !!!!!
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It lays 100 eggs beacus ethe chances of srvival is very less
Fish lay a large number of eggs because only a few of them, out of thousands, will be fertilized and produce a fish. This is because they are fertilized outside of the body and are highly sensitive to temperature changes and external factors but egg of hen has a outer protection so it is not so sensitive as of fishes and frogs