Question

The formula K2S indicates that

Answer 1

Remember potassium K has one valence electron while sulfur S has 6 valence electrons.

Metals lose electrons while non metals gain them.

Sulfur needs 2 electrons to fill its octet and have 8 electrons. So it does this by forming a bond with each potassium atom or rather 3 of them.

Answer 2

Sorry that was a typo it forms a bond with 2 potassium atoms not three.

That's why it's K2S

Potassium likes to lose a electron because in doing so it has a more stable electron configuration.