# Potassium Atom can act as reducing agent, yet ion cannot?

I am currently looking through a revision sheet, however it has caught me on a question 'Explain why a potassium atom can act as a reducing agent yet a potassium ion cannot'.

I have done brief searches, however none have given the answer I'm looking for. So please, why is this?

Also, if the explanation doesn't already include it; is this only the case with Potassium, and how is this to be determined? (How is it known whether it is referring to a cation or anion?)

Thanks,

The ability of K to act as a reducing agent is mainly due to its electronic structure. $K = [Ar] 4s^1$ . In this case, such atom tends to donate his $4s^1$ electron (acting as a reducing agent). This is due to the gain in energy that produces to have its octet complete and stay in the cationic form $K^{+}=[Ar]$ which is quite more stable that the pure element one.