Answer:
Oxygen
Explanation:
The electronegativity is a measure of the afinity an element has to the electrons. Barium, Francium and iron have a trend to make cations by losing electrons, so the afinity is low. On the other side, oxygen keeps the electrons of other elements forming anions.
To be more concrete, the electronegativity values from the periodic table:
- Iron: 1.8
- Francium: 0.7
- Oxygen: 3.4
- Barium: 0.9
