(i) when we overeat excess of acid is produced in the stomach which causes burning sensation.
(ii) Washing soda is sodium carbonate decahydrate which when exposed to air loses 10 molecules of water and changes to white powder.
(iii) Sodium chloride is a salt of strong acid HCL and strong base NaOH, so it is neutral.
Sodium carbonate is a salt of weak acid H2CO3, and strong base NaOH, so it is basic.