Question

Why does Acrisius place his daughter and her son in a sealed chest and then put them out to sea?

Answer 1

Apollo told Acrisius that his daughter will have a child that will try to kill him.

Answer 2

Apollo once told Acrisius that his daughter will have a child which will try to kill him. In his anger and frustration, when Acrisius sees a small baby on his daughter's lap, he seals them in a chest and puts them out to sea.