Question

What's the difference between a dwarf planet and a protoplanet?

Answer 1

The difference between a Dwarf Planet and a Protoplanet is:

Explanation:

Dwarf Planet:

A Dwarf Planet is in a sense a small planet that has sufficient gravity to form itself into a almost spherical shape, orbits the sun but hasn't cleared its neighbourhood, meaning its orbit is shared with debris such as asteroids (Asteroid Belts).
If it did clear its neighbourhood it would be classified as a planet.

Protoplanet:

A Protoplanet is basically a planet (Dwarf or normal) in the making. The difference is that a Protoplanet doesn't have an almost spherical shape due to insufficient gravity which relates to its size.

Protoplanets, just like Dwarf Planets haven't cleared its neighbourhood and is usually found in the vicinity of asteroid belts, therefore over-time the Protoplanet can collide with asteroids and become larger to ultimately become a Dwarf Planet and even possibly a Planet.

It is important to note that asteroids aren't necessarily classified as Protoplanets, because in order to be a Protoplanet it must undergo melting such that there is layer formation due to different densities as you go inwards towards the centre. (Much like the layers of the Earth for example).

So to summarize a Protoplanet is basically a smaller version of a Dwarf Planet.

Hope I helped :)