Which planet's day is longer than its year?

Venus. It takes about 243 Earth days to turn once on its axis and about 225 to go round the Sun, so a Venusian day is longer than a Venusian year - and it turns backwards, so the Sun rises in the west.

The combination produces a solar day - noon to noon - of about 117 Earth days, which is shorter than either figure, because the backwards rotation and the orbital motion work against each other. There are therefore about two sunrises per Venusian year, which is a sentence that takes a moment.

Why it rotates so slowly and backwards is unresolved. A giant impact is the old explanation; the better-supported modern one is that the atmosphere, which rotates around the planet in four days and drags enormously, exerted a tidal torque on the solid body that braked the original spin and reversed it. That atmosphere also makes the surface hotter than Mercury's despite Venus being nearly twice as far from the Sun.