What kind of reaction is this?

Single replacement

Explanation:

Chemical equation:

2Al(NO₃)₃ + 3Ca    →    3Ca(NO₃)₂ + 2Al

Single replacement:

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

AB + C → AC + B

All other options are incorrect because,

Double replacement:

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

AB + CD → AD +CB

Synthesis reaction:

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

Decomposition reaction:

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

AB → A + B

Combustion reaction:

Reaction in substance react with oxygen and form carbon dioxide and water.