8.On what basis did God predestine us for adoption as His sons?

His pleasure and will.

Paul expresses the same thought in the Book of Romans:

For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren (Romans 8:29).

Again:

And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory (Romans 9:23).