S is the chemical symbol of sulfur.
The symbol (s) indicates a solid state in a chemical equation.
You would denote a solid substance in a chemical equation by writing "(s)" next to the chemical formula of the solid. For example, if you want to indicate that sodium chloride is a solid in a chemical equation, you would write NaCl(s).
The reactants in a chemical equation are the substances that are present at the start of a reaction and are used up during the course of the reaction. If you provide the specific chemical equation, I can help you identify the reactant(s).
The chemical equation for germanium plus sulfur is Ge + S -> GeS.
PbCl2 is the molecular formula (not chemical equation) of lead(II) chloride.
The chemical equation for the reaction between aluminum and steam is 2Al(s) + 3H2O(g) → Al2O3(s) + 3H2(g).
The meaning of (s) is solid.
The balanced chemical equation for the reaction of calcium carbonate (CaCO3) is: CaCO3(s) -> CaO(s) + CO2(g)
Br- is chemical symbol for a bromide anion. It is not an 'equation', it can be a part of a chemical equation, like in this precipitation reaction (example) Ag+(aq) + Br-(aq) --> AgBr(s) .
SO2: sulfur dioxide S + O2 --> SO2
The balanced chemical equation for the formation of Fe2O3 from Fe and O is: 4Fe + 3O2 -> 2Fe2O3
The new substance(s) formed during a chemical reaction will appear to the right of the "yield" arrow in an equation. This/these is/are the product(s) of the reaction.