Choose the correct answer from the options given below: Aqua regia is a mixture of: (a) dilute hydrochloric acid and concentrated nitric acid (b) Concentrated hydrochloric acid and dilute nitric acid (c) Concentrated hydrochloric acid [1 part] and concentrated nitric acid [3 parts] (d) Concentrated hydrochloric acid [3 parts] and concentrated nitric acid [1 part]