To find the unit rate in revolutions per day, we need to calculate how many revolutions occur in one day.
The planet spins 2 revolutions every 2 days, so we can calculate the rate per day as follows:
\[ \text{Revolutions per day} = \frac{2 \text{ revolutions}}{2 \text{ days}} = 1 \text{ revolution per day} \]
Therefore, the unit rate is:
\[ \boxed{1} \]