Hint: Antacids are a type of drug, from the name itself we can say that it is relatable to the acidity level. So, there will be usage of base. Thus, identify the bases in nature.
Now, first let us define antacids. These are used in the treatment of acidity caused in the stomach.
If we say when the excess of acid is produced in the stomach mainly, there will be a feeling of irritation, and it will eventually cause pain in the stomach.
Thus, we can say from the name too, antacids i.e. anti and acids, which means it shows the opposite effect to acids.
Therefore, sometimes the acidity causes ulcers in the stomach.
So, if we say antacids are opposite of acids, it means that antacids are the base in nature.
Now, if we look at the given options. The first is sodium hydroxide. It is a base, not an acid, but it is not used as an antacid.
The second we have sodium bicarbonate; it is used as an antacid. Moreover, we can say that it is a quick reliever antacid.
Now, the third is magnesium hydroxide, it is also used as an antacid with the sodium hydrogen carbonate.
Talking about the fourth i.e. urea. As we know, urea is the excretion product of human beings, or many living organisms. So, it cannot be used as an antacid.
In the last, we can conclude that the examples of antacids are sodium bicarbonate, and magnesium hydroxide.
So, the correct answer is “Option B and C”.
Note: There could be a confusion that if the sodium hydroxide is a base, then why it is not used as an antacid. So, when it was used as an antacid, then it was proved to be harmful for the digestive tract. Thus, it is not used as an antacid in the individual form.