Potassium dichromate acts as a strong oxidizing agent in acidic solution. During this process, the oxidation state changes from :

Reaction of thionyl chloride with white phosphorus forms a compound [A], which on hydrolysis gives [B], a dibasic acid. [A] and [B] are respectively :

Compound A reacts with NH$$_4$$Cl and forms a compound B. Compound B reacts with H$$_2$$O and excess of CO$$_2$$ to form compound C which on passing through or reaction with saturated NaCl solution forms sodium hydrogen carbonate. Compound A, B and C, are respectively :

$$\mathrm{K_2Cr_2O_7}$$ paper acidified with dilute $$\mathrm{H_2SO_4}$$ turns green when exposed to :