(i) As K2CO3 is a salt of a strong base (KOH) and weak acid (H2CO3), it hydrolyses in water to give alkaline solutions. They have pH more than 7, hence it will have no effect on blue litmus.
(ii) KCl is a salt of a strong acid (HCl) and a strong base (KOH). Hence it’s aqueous solution will be neutral in nature and will have no effect on blue litmus.
(iii) NH4NO3 is a salt of a strong acid (HNO3) and weak base (NH4OH), it hydrolyses in water to give an acidic solution. They have pH less than 7, hence will turn blue litmus red.