1) What is the charge on the ion that Selenium forms in an ionic compound?

Question

I am not sure about this.

2) What noble gas is isoelectronic with this ion.

I was thinking Krypton because it is a noble gas and it is the closest to Selenium but I am not sure.

3) What other ions are isoelectronic with this noble gas?

I was thinking Bromine since again it is closest to Krypton.

Answer 1

1) What is the charge on the ion that Selenium forms in an ionic compound?
I am not sure about this.
Look on the periodic table. Where is Se. It is in group 16(or group VIIA depending on the system you are using). So it is like O and S. That means it has six electrons in the outer shell so it want to gain two more electrons. That gives the ion a -2 charge. Oxygen behaves the same way. So does S.

2) What noble gas is isoelectronic with this ion.

I was thinking Krypton because it is a noble gas and it is the closest to Selenium but I am not sure.
Of course it's Kr

3) What other ions are isoelectronic with this noble gas?

I was thinking Bromine since again it is closest to Krypton.
Sure. Br^-(bromide), Se^2-(selenide), As^3- (arsenide)although As usually doesn't gain three electrons.

Answer 2

well your right they are in group 16 . but Br bromine wouldn't be because it has negative 1 charge and selenium has negative 2. But your right about krypton being isoelectronic with selenium.