Frequently nitro powered planes are refered to as gas planes. A more common term for nitro powered planes is glow powered or glow planes.

Gas planes use gasoline as a fuel and are typically larger planes (80"+ wingspan ) with engines of 20 cc and larger.

Nitro is a mixture of methanol, nitromethane and oil. MOST nitro engines are under 1.2 cubic inch displacement, although there are some nitro powered engines as large as 2.1 cubic inch displacement (single cylinder - multi cylinder engines can go higher in displacement).

MOST nitro powered planes are typically less than 80" wingspan.

Nitro, or glow fuel is not as hazardous as gasoline, however it is more expensive. Where gas engines use an ignition system and a sparkplug to ignite the gasoline, a glow powered engine uses a glow plug (similar to what is used for car/truck diesel engines). The glow plug is powered by an external 1.5 volt battery. Once the engine starts the battery is disconnected and the heat from the engine keeps the glow plug ignited so the engine stays running.

Glow fuel requires a different tubing from the fuel tank to the engine than gasoline powered engines. Glow fuel has oil in the mixture, so the exhaust is oily and does require that the plane be cleaned at the end of the day. Glow fuel also requires a different type of paint than gasoline. Glow fuel paints are typically acrylic based or epoxy paints, otherwise the exhaust residue softens and destroy the paint in very short order.

Hope this answers most of your questions.