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

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