Final answer:
In the half-reaction 2 Na → 2 Na⁺, two electrons are lost as each sodium (Na) atom loses one electron to become a sodium ion (Na⁺).
Step-by-step explanation:
The half-reaction 2 Na → 2 Na⁺ shows that sodium (Na) is losing electrons to form sodium ions (Na⁺). Since each sodium atom loses one electron, a total of two electrons are lost in this process. This half-reaction represents an oxidation process, where oxidation is defined as the loss of electrons. The oxidation number of sodium increases from 0 to +1 after losing an electron, signifying an oxidation process. In redox reactions, these electrons would be gained by another species undergoing reduction.