Identifying ions via qualitative tests Steps:

• HCl test shows P releases CO2 (milky limewater), confirming CO3^2- in P; Q shows no change, ruling out CO3^2- in Q.
• Ba(NO3)2 test after acidification gives no precipitate for P (no SO4^2-); white precipitate for Q indicates SO4^2- (soluble in excess distinguishes from other anions).
• NaOH and NH3 tests yield green precipitate insoluble in excess for Q, identifying Cr^3+; no change for P fits Li+ (Group 1 cation).
• Flame test gives lilac for P, matching Li+; Q not tested, consistent with Cr^3+ and SO4^2-. Why C is correct:
• C assigns Li2CO3 to P (CO3^2- reacts with acid, no SO4^2-, no hydroxide precipitate, lilac flame) and Cr2(SO4)3 to Q (SO4^2- gives BaSO4, Cr^3+ forms green Cr(OH)3 insoluble in excess bases). Why the others are wrong:
• A: P as K2SO4 gives no CO2 with HCl; Q as Cr2(CO3)3 reacts with HCl to release CO2.
• B: Q as Fe2(SO4)3 forms brown Fe(OH)3, not green precipitate with NaOH or NH3. Final answer: C