In which of the following octahedral complexes of Co (at. no. 27), will the magnitude of $$\Delta _o$$ be the highest?

The coordination number and the oxidation state of the element ‘E’ in the complex [E(en)₂(C₂O₄)]NO₂ (where (en) is ethylene diamine) are, respectively,

The organic chloro compound, which shows complete stereochemical inversion during a S_N2 reaction, is

Phenol, when it first reacts with concentrated sulphuric acid and then with concentrated nitric acid, gives