What is the charge of an atom with 21 protons and 20 electrons?

Positive

Explanation:

If an atom has more protons than electrons, its charge with be positive. Protons have a positive charge, and electrons have a negative charge.

adding or remove a gaseous reactant or product changes the concentrations. if the concentration of reactant or product is increased, the system will shift away from the side in which concentration was increased (i.e. if the concentration of reactants is increased, the system will shift toward the products. if more products are added, the system will shift to form more reactants). conversely, if the concentration of reactant or product is decreased, the system will shift toward the side in which concentration was decreased (i.e. if reactants are removed, the system will shift to form more reactants. if the concentration of products is decreased, the equilibrium will shift toward the products).

explanation:

there is none because earth is stationary and flat.