Kjeldahl's method cannot be used for estimation of nitrogen in $(i)\; C_6H_5NO_2 ;\; (ii)\;Pyridine; \;(iii)\;C_6H_5 - N = N -C_6H_5 ;\;(iv)\;C_6H_5NHCOCH_3$

Question

$(a)\;(i),(ii) and\;(iii) \\ (b) \; (ii),(iii)\;and \;(iv) \\ (c) \;(i),(ii)\;and \;(iv) \\ (d)\;(i),(iii)\;and (iv)$