Is 4 Fe + 3 O2 --> 2 Fe2O3
balanced?

Yes the given equation is balanced.

Explanation:

Chemical equation:

Fe + O₂       →     Fe₂O₃

Balanced chemical equation:

4Fe + 3O₂       →     2Fe₂O₃

There are four iron and six oxygen atoms on both side of equation thus the given equation is balanced.

The given reaction also follow the law of conservation of mass.

According to the law of conservation mass, mass can neither be created nor destroyed in a chemical equation.

This law was given by French chemist  Antoine Lavoisier in 1789. According to this law mass of reactant and mass of product must be equal, because masses are not created or destroyed in a chemical reaction.

This reaction is synthesis reaction:

Synthesis reaction:

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

A + B      →   AB

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).