What will you observe when :
(i) Red litmus paper is introduced into a solution of sodium carbonate.
(ii) A methyl orange drop is added to dilute hydrochloric acid.
(iii) A drop of phenophthalein is added to the solution of lime water.
(iv) Blue litmus is introduced into a solution of ferric chlorede.

Explanation

(i) The colour of the litmus paper will change to blue. Sodium carbonate `(Na_(2)CO_(3))` dissolves in water to from sodium hydroxide and carbonic acid `(H_(2)OandCO_(2)).` The solution is of basic nature since dosium hydroxide is a strong bases and carbonic acid is a weak acid.
`Na_(2)CO_(3)(aq)+H_(2)O(aq)to2NaOH(aq)+underset((CO_(2)+H_(2)O))(H_(2)CO_(3)(aq))`
(ii) In the acidic solution, the colour of methyl organe will change to raddish.
(iii) Lime water contains traces of calcium hydroxide, `Ca(OH)_(2).` It is therefore, basic in nature. The colour of phenolphthalein will become pink.
(iv) Ferric chloride `(FeCl_(3))` solution on reacting with water will form ferric hydroxide and hydrochloric acid. Since the acid is strong, the solution will be acidic. Therefore, the colour of blue litmus will change to red.
`FeCl_(3)(aq)+3H_(2)O(l)tounderset(("weak"))(Fe(OH)_(3))(s)underset(("strong"))(3HCl(aq))`