Which of the following compounds will be suitable for Kjeldahl's method for nitrogen estimation?

Kjeldahl’s method works only when the nitrogen present in an organic compound is first converted to $$\left(NH_4\right)_2SO_4$$ by boiling the substance with excess conc. $$H_2SO_4$$. For this to happen, the nitrogen atom must be present as an -NH, -NH2, -CONH-, -CNH- etc., i.e. it must be bonded only to carbon and/or hydrogen (and, after protonation, be able to form $$NH_4^+$$).
The method fails whenever nitrogen is present in an oxidation state or environment that prevents the formation of ammonium ion. Thus compounds containing

• a nitro group $$(-NO_2)$$,
• azo / diazo linkages $$(-N=N-,\; -N_2^+Cl^-)$$,
• nitrile $$(-C\equiv N)$$, isonitrile $$(-NC)$$,
• nitroso $$(-NO)$$, or
• ring nitrogen as in pyridine, quinoline etc.

are not estimated correctly by the Kjeldahl procedure.

Keeping this rule in mind, inspect the four choices (structures as given in the paper):

Therefore, the only compound that fulfils the requirement is the amide in Option C.

Final answer: Option C which is: acetamide $$\left(CH_3CONH_2\right)$$.