अवक्षेपण द्वारा विभिन्न धनायनों (cations) की पहचान के लिए आर्द्र परीक्षणों (wet tests) में, Ba2+ धनायनों का पता किसका अवक्षेप प्राप्त करके लगाया जाता है?

In a test tube containing a salt, a few drops of dilute H2SO4 were added, which evolved colorless vapors with a characteristic vinegar smell. The vapors turned moist blue litmus paper red. Identify the anion present in the salt:

The functional group that can be identified through phthalein dye test is: