In your choices, the best answer is the mass of the reactants and the mass of the products are no equal. The chemical equilibrium can take place in a close system and can not be affected by catalyst and is a reversible reaction. The best describe should be the concentration of reactants and products are constant.
The combustion of a substance forming or breaking bonds mixing two substances.
Away from you. This is known as the Doppler affect. It basically states that if an object is moving away from you the streching of the wave causes a red shift and if the object is moving towards you the compression of the waves causes a blue shift.
