Phenol on treatment with CO₂ in the presence of NaOH followed by acidification produces compound X as the major product. X on treatment with (CH₃CO)₂O in the presence of catalytic amount of H₂SO₄ produces:

The trans-alkenes are formed by the reduction of alkynes with

The major product of the following reaction is:

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