How do we know where to put astatine in the periodic table if most of its properties are unknown?

Based on its chemical properties, identify the position of each chemical family on the periodic table.

How many oxygen atoms are there in 3.15 moles of hcl manganese (iv) oxide, mno2

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium