Answer:
a. H₂O. This is the oxidizing agent. It was reduced to oxidize the Na.
Explanation:
A redox reaction: 2Na(s)+2H₂O(l)→2NaOH(aq)+H₂(g)
Sodium changes from 0 (oxidation state) to +1. It has been oxidized.
It has released and electron.
H⁺ from water has gained an electron, so it changed the oxidation state from +1 to 0. As the oxidation state has decreased, the element was reduced. So it won electrons.
In conclussion the water was reduced to hydrogen at ground state, to oxidized the Na. That's why H₂O is the oxidizing agent.
