What is the nature of the aqueous solution of lemon juice?

What are antacids? Explain their role in providing relief from stomach ache.

$(a)$ $A$ salt is produced by the reaction between an acid and a base. Identify the acid and the base from which the following salts have been formed:
$(i)$ $Na_{2}SO_{4}$
$(ii)$ $NH_{4}Cl$
$(iii)$ $KNO_{3}$
$(iv)$ $NaCl$

Which of the following salts does not contain water of crystallisation?

At which value of $pH$ of the inner side of the mouth does the decay of teeth take place?

$15 \, mL$ 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?