What leads to the formation of an ionic bond with Hg raised to the 2 plus power ?

An ionic bond forms through attraction between oppositely charged ions. Hg²⁺ has a positive charge, so it is attracted to SO₄²⁻, which has a negative charge; together they can form the neutral compound HgSO₄. A noble gas is neutral, while a group 1 element and NH₄⁺ are positively charged, so they are not the matching oppositely charged ion.

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