How does basic toothpaste help prevent tooth decay?

Correct answer: It neutralises acids formed in the mouth

The governing concept is neutralisation. Bacteria acting on food residues in the mouth produce acids, and these acids can attack tooth enamel and begin decay. Basic toothpaste supplies alkaline substances that react with and reduce the acidity. Therefore option A is correct. Making teeth acidic or merely changing colour does not prevent acid damage, and saliva cannot be converted into a gas by toothpaste.