'A' and 'B' are compounds of sodium, 'A' is thermally stable. On passing CO2 through the solution of 'A', 'B' is formed. 'B' on heating gives 'A'. Phenolphthalein is added to the aqueous solution of 'A' and 'B'. The colours of solutions are

aQ.Na2CO3 is more basic than aQ.NaHCO3Reason  aQ.NaHCO3 & Na2CO3 both alkaline gives yellow colour with basic indicator like methly orangeaQ.Na2CO3 being strong base gives pink colour with the acid indicator phenolyphthaleinaQ.NaHCO3 is weakly alkaline and still contains acidic hydrogen and can't ionise the phenophthalein indicatiorTherefore, phenolphthalein indicator is colour less in aQ.NaHCO3 solution, where as phenolphthalein indicator is becomes pink colour in aQ.Na2CO3 solution