Reaction
a chemical reaction that has the general formula of ab - a + b is best classified as a
synthesis
polymerization
decomposition
oxidation
replacement

Decomposition.

Explanation:

Decomposition reaction:

It is the reaction in which one reactant is break down into two or more product.

AB → A + B

While other options are incorrect because,

A) Synthesis:

Synthesis reaction:

It is the reaction in which two or more simple substance react to give one or more complex product.

A+B → AB

Polymerization:

It is the reaction in which monomers are combine to form long chain polymer.

Oxidation:

Oxidation involve the removal of electrons and oxidation state of atom of an element is increased.

Replacement:

Single replacement:

It is the reaction in which one elements replace the other element in compound.

AB + C → AC + B

Double replacement:

It is the reaction in which two compound exchange their ions and form new compounds.

AB + CD → AC +BD

a plasma is a warm ionized gasoline consisting of approximately equal numbers of definitely charged ions and negatively charged electrons. the characteristics of plasmas are notably unique from the ones of ordinary neutral gases in order that plasmas are considered a awesome "fourth kingdom of remember."