Which reaction below represents a balanced, synthesis chemical reaction?

A) N2 + 3H2 -> 2NH3

B) Al + Br2 -> AlBr3

C) 2HBr -> H2 + Br2

D) 2H2O -> H2 + O2

A) N₂ + 3H₂   →  2NH₃

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

From given list of reaction option A is correct.

N₂ + 3H₂   →  2NH₃

This reaction represent the synthesis reaction in which nitrogen and hydrogen react to form ammonia. The given reaction is also balanced.

There are equal number of atoms of all elements present on both side.

While all other options are in correct because

B) Al + Br₂  →  AlBr₃

This is synthesis reaction but its not balanced.

C)  2HBr  →   H₂ + Br₂

D) 2H₂O   →   H₂ + O₂

These two reactions are not synthesis reaction. These are decomposition reactions.

Decomposition reaction:

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

AB → A + B