Step 1: What is being asked.
We need the planet that takes only 88 Earth days to go once around the Sun.
Step 2: A simple rule of planets.
The closer a planet is to the Sun, the shorter is its path and the faster it moves. So the nearest planet finishes its trip the quickest.
Step 3: Check the options.
Jupiter and Mars are far from the Sun, so they take much longer than 88 days. Venus also takes about 225 days, which is more than 88.
Step 4: The nearest planet.
Mercury is the planet closest to the Sun. Because of this it has the shortest year of all planets.
Step 5: Match the number.
Mercury completes one revolution around the Sun in about 88 Earth days, which is exactly what the question states.
Step 6: Conclusion.
So the planet with an 88 day year is Mercury.
Answer: Mercury