I am an element. I have a high electron affinity (highly negative value) and my atomic number is X. The element with atomic number X - 1 has
a lower ionisation energy and a lower electron affinity. The element with
atomic number X + 1 has a higher ionisation energy and basically no
electron affinity (positive value). I am toxic in my elemental state, but I
am very commonly found in my nontoxic ionic form. Within my group,
I have the second highest ionisation energy. Who am I? (Support each
step of your reasoning.)​