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 :

Which of the Phosphorus oxoacid can create silver mirror from $$\mathrm{AgNO_3}$$ solution?

In liquation process used for tin (Sn), the metal :