Let’s define antacids first.

ANTACIDS: Substances which remove the excess acid and raise the pH to appropriate level in stomach are called antacids.

Options (ii) Sodium hydrogencarbonate and (iv) Magnesium hydroxide are administered as antacids. Although these treatments control only symptoms, and not the cause. Hence the patients can’t be treated easily.

Sodium carbonate [option (i)] is used as water softener, food processing aid, pH modifier swimming pool chemical and an electrolyte. (mild preservative)

Aluminium carbonate [option (iv)] is used in the food industry as a raising agent for the flat baked goods, such as cookies and crackers. (food additive).

Hence, options (ii) and (iii) are correct and options (i) and (iv) incorrect.