With reference to aqua regia, choose the correct options(s). A Aqua regia is prepared by mixing conc.HCl and conc.HNO3 in 3:1 (v/v) ratio. B The yellow colour of aqua regia is due to the presence of NOCl and Cl2. C Reaction of gold with aqua regia produces an anion having Au in +3 oxidation state. D Reactions of gold with aqua regia produces NO2 in the absence of air.

Correct option is D. Reaction of gold with aqua regia produces an anion having Au in +3 oxidation state (1) Au + 4H⁺ + NO₃⁻ + 4Cl⁻ → [AuCl₄]⁻ + NO + 2H₂O (2) 3HCl + HNO₃ → NOCl(g) + Cl₂(g) + 2H₂O. Product formed produce yellow colour (3) Aqua regia is prepared by mixing conc.HCl and conc.HNO₃ in 3:1 (v/v) ratio is a factual statement (4) Oxidation state of Au in [AuCl₄]⁻ is +3 as it is in the formed Au³⁺