Plasma refers to very hot matter such that the electrons in matter are ripped away from the atoms leading to the formation of an ionized gas.
We know that the carriers of electricity are charged particles. Any state of matter that has an abundance of charge carriers will definitely be a good conductor of electricity.
Therefore, plasmas are good conductors of electricity because they have a lot of mobile charged particles.
By its very definition, a chemical property is one which is exhibited as a result of a chemical reaction. This may happen during or after the reaction. This is because in a chemical reaction there is a transformation in the physical composition of the components and this directly affects its chemical properties.