Electrochemistry — practice question

The electronic configurations of atoms of four elements are shown. Which element is the most powerful oxidising agent?

• A$1s^2 2s^2 2p^5$
• B$1s^2 2s^2 2p^6 3s^2$
• C$1s^2 2s^2 2p^6 3s^2 3p^5$
• D$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$