The bronze basin and its stand for the tabernacle were made from what?

Answer: The serving women's mirrors

The bronze basin and its stand were made from the mirrors (KJV: "lookingglasses") of the women who served at the entrance to the Tent of Meeting.

“Next he made the bronze basin and its stand from the mirrors of the women who served at the entrance to the Tent of Meeting.”— Exodus 38:8 (BSB)