Venus has the slowest rotation rate.
It takes Venus 243.7 Earth days to rotate once.
Planet Period
Venus 243.7 (Earth) days
Mercury 58.8 days
Pluto 6.4 days
Mars 24.6 hours
Earth 23.9 hours
Uranus 17.2 hours
Neptune 16.1 hours
Saturn 10.7 hours
Jupiter 9.9 hours
Interesting . . . the largest planet rotates the fastest.
I wonder why that is.