Assertion (A) : Non-stoichiometric compounds are called Bertholide compounds. `NaCl` and `KCl` crystal, when heated in an atmosphere of `Na` and `K` varpours, respectively, they impart violet and yellow colours to `NaCl` and `KCl`, respectively. Reason (R ) : Metal excess defect is due to the presence of extra cations atg the interstitial sites. The excess metal ions move to the interstitial sites and the electrons to the neighbouring sites. The colour results byt the excitation of these electrons by absorbing suitable energy from visible light. When the excited electroon comes back to the ground state, there is emission of radiation in the visible region and gives complimentary colour.A. If both `(A)` and `(R)` are correct, and `(R)` is the correct explanation of `(A)`B. If both `(A)` and `(R)` are correct, but `(R)` is not the correct explanation of `(A)`C. If `(A)` is correct, but `(R)` is incorrect.D. If both `(A)` is incorrect, but `(R)` is correct.