Aqueous sodium carbonate turns red litmus blue. What nature does this show?

Correct answer: Basic

The governing indicator rule is that a basic solution changes red litmus to blue. Sodium carbonate dissolves in water and undergoes hydrolysis, producing a solution with alkaline character. The observation therefore identifies its aqueous solution as basic, so option B is correct. An acidic solution would turn blue litmus red, a neutral solution would show no such change, and “metallic” is not a solution nature indicated by litmus.