Here's how to figure out which atom is reduced in the reaction of sodium (Na) with oxygen (O₂):

Understanding Oxidation and Reduction

* Oxidation: Loss of electrons

* Reduction: Gain of electrons

The Reaction

Sodium reacts with oxygen to form sodium oxide (Na₂O):

4 Na + O₂ → 2 Na₂O

Analyzing the Changes

* Sodium (Na): Sodium starts as a neutral atom (Na). In sodium oxide (Na₂O), it has a +1 charge. This means sodium *loses* an electron and is oxidized.

* Oxygen (O₂): Oxygen starts as a diatomic molecule (O₂). In sodium oxide (Na₂O), it has a -2 charge. This means oxygen *gains* electrons and is reduced.

Conclusion

In the reaction of sodium with oxygen, oxygen (O₂) is reduced.