Basic solutions turn red litmus paper blue. The salt of a weak acid and a strong base gives a basic solution. So, the given salt X is the salt of a weak acid and a strong base.
Example: When sodium carbonate is dissolved in water, it sets hydrolysed to some extent and forms sodium hydroxide and carbonic acid.
Being a strong base, sodium hydroxide is fully ionised and gives a large amount of hydroxide ions (OH) Carbonic acid is a weak acid which is only slightly ionised and hence, gives a small amount of' hydrogen ions (H+). The H+ ions produced by carbonic acid neutralises only a small amount of OH ions produced by sodium hydroxide and the rest amount of OH- ions are present in the solution. Hence, the Na2CO3 solution is basic in nature. It turns red litmus blue.
