This is an image of the surface of Pluto.
Image from: NASA
Pluto's Surface and Interior
Data from 1999 suggests that the surface of Pluto is made of two different parts. It has an icy part and a non-icy part (the non-icy part may be some sort of rock). Scientists are fairly certain the icy part is made of frozen nitrogen, but also contains smaller amounts of frozen carbon monoxide and methane.
Pluto is so far away that is it very hard to see the planet, so we can't yet tell how much of the surface is covered with ice, and how much is covered with something which is not ice (the possibly rocky part). It will take a mission to Pluto to sort some of these things out!
Scientists are certain that the surface of Pluto is good at reflecting light, which suggests that it is mostly made of the icy component - and that means Pluto's surface is mostly composed of nitrogen.
The interior of Pluto is probably similar to that of major icy moons such as Ganymede. (Pluto is actually smaller than Ganymede, even though Ganymede is a moon).
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