I believe it is Mercury.
Mercurys core is 75 percent of its planet. Its core is made of Iron.
You might want to do more research though I am not Exactly sure.
mercury
Define Core Diameter Mismatch
Yes Pluto has a core. It is believed that it's rocky material would have settled into a dense core surrounded by a mantle of ice. The diameter of the core should be around 1,700 km, 70% of Pluto's diameter.
Remembering that there is an inner core inside the outer core - the radius of the outer core/mantle boundary is about 3,400 km. (the diameter is twice the radius).
The diameter od mercurys core is 3,600 km, 2,235 miles.
Jupiter is the largest and most massive planet of the Solar System -- although only about 18% larger than Saturn in diameter, it contains 2.5 times the mass of all of the other planets combined.Earth is the densest planet. Although its core is much less dense than those of Jupiter and Saturn, most of the volume of the gas giants is atmosphere.
Currently HAT-P-1 is the largest planet ever discovered. Its a gas giant with a diameter 2.8x of Jupiter's. Its also the least dense planet found. Its only 1/4 the density of water making the planet its self lighter than a cork. Like Saturn it can float in water only it would float 3x highers. It's gravity is believed to be so strong that no rocky core. The planet its self completely changes the way how gas giants are believed formed.
in the outer core it has a 6960 km.While the inner core is about 2440 km. in diameter
Pulsar planet.
The dwarf planet Pluto is believed by astronomers might be the core of a much larger planet
core
The core of Uranus is in the center of the planet.