(i) The reaction of Cu metal with dil. HNO3 gives NO, whereas the conc. HNO3 gives NO2.
To get molar ratio of 2 : I of NO and NO2 equation 'a' is multiplied by 2 and then on addition with equation (b), we get
(ii) When Na2CO3 is added to a solution of CuSO4, we get the ppt. of Cu(OH)2, and solution of Na2SO4, while CO2 is evolved.
(iii) Potassium dichromate and concentrated HCI are heated together, therefore KCl, CrCl3, water and chlorine gas are formed.