Question

Kjeldahl's method cannot be used for:

• A. $PhNHCOPh$
• B. $PhN{O}_2$
• C. Azobenzene
• D. Pyridine

Answer 1

Answer: (B), (C), (D)

The correct options are
A $PhN{O}_2$
C Azobenzene
D Pyridine
Kjeldahl's method is a method for the quantitative determination of nitrogen contained in organic substances as well as nitrogen contained in unorganic compounds ammonia and ammonium.

But, Kjeldahl's method cannot be used for nitrogen determination of compounds having nitro group or azo-group or nitrogen present in rings as the nitrogen of these compounds cannot be converted to ammonium sulphate $(N{H}_4{)}_{2}S{O}_4$ under the condition of this method.

Hence, option A,C and D.