Answer is: new substance.
For example, synthesis chemical reaction: Ba + F₂ → BaF₂.
Synthesis reaction is a type of reaction in which multiple reactants combine to form a single product.
New substance, barium fluoride is formed, with different chemical and ohysical properties than reactants (barium and fluorine).
In barium fluoride, barium has oxidation number +2 and fluorine has oxidation number -1, so compound has neutral charge.
