1. A radical is a kind of a molecule that contains an unpaired electron in the atomic orbital and can exist independently.
2. A chemical equation is just an equation representing the reaction between the reactants and products. The number of atoms is not equally distributed on the reactants and products side.
H2 + O2 → H2O
Here on both sides, there are 2 hydrogen atoms but on the reactant side, one oxygen atom is present whereas on the product side is one oxygen atom
A balanced equation is a chemical equation that has the equal number of atoms on reactants and products side.
2Mg + O2 → 2MgO
This equation has 2 Mg atoms and 2 Oxygen atoms on both sides