Identify the type of reaction: A + B> AB single-
displacement
combustion
decomposition
synthesis

Synthesis reaction:

Explanation:

Synthesis reaction:

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

A + B      →     AB

All other options are incorrect because,

Single replacement:

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

AB + C → AC + B

Decomposition reaction:

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

AB → A + B

Combustion reaction:

In combustion reaction substances are react with oxygen and produces carbon dioxide and water.