Identify which element I am?

I have a high electron affinity. The element on my left in the Periodic Table has a smaller electron affinity. The element on my right in the Periodic Table has a higher ionisation energy and essentially no electron affinity. I am toxic in my elemental state, but I am very commonly found in my non-toxic ionic state. Within my group, I have the highest ionisation energy.

Type the element symbol for your answer in the box provided. For example if you think the answer is hydrogen you should type " H "