Which enzyme becomes active in the stomach during a low $pH$ value?

To protect against tooth decay,we are advised to brush our teeth regularly. The nature of the toothpaste commonly used is:

Write true or false for the following statement:
The process of dissolving an acid or a base in water is a highly exothermic process.

When a $pH$ paper is dipped in an aqueous solution,it turns blue. What is the approximate $pH$ value of that solution?

Acid and base react with each other and form salt and water. What is this reaction called in scientific language?

$15 \, mL$ of water and $10 \, mL$ of sulphuric acid are to be mixed in a beaker.
$(i)$ State the method that should be followed with reason.
$(ii)$ What is this process called?