The correct statement(s) among the following is/are (i) The vibrational energy levels of a real diatomic molecule are equally spaced. (ii) At 500 K, the reaction A $\rightarrow$ B is spontaneous when $\Delta H = 18.83\ \mathrm{kJ\,mol^{-1}}$ and $\Delta S = 41.84\ \mathrm{J\,K^{-1}\,mol^{-1}}$. (iii) The process of fluorescence involves transition from a singlet electronc state to another singlet electronic state by absoprtion of light. (iv) When a constant P is added to each of the possible energies of a system, its entropy remains unchanged.