What effect does an increase in the concentration of $H^{+}(aq)$ in a solution have on the $pH$ of the solution?

Match the acids given in Column $(A)$ with their correct source given in Column $(B)$.

Column $(A)$	Column $(B)$
$(a)$ Lactic acid	$(i)$ Tomato
$(b)$ Acetic acid	$(ii)$ Lemon
$(c)$ Citric acid	$(iii)$ Vinegar
$(d)$ Oxalic acid	$(iv)$ Curd

$A$ sulphate salt of a Group $2$ element of the Periodic Table is a white,soft substance,which can be moulded into different shapes by making its dough. When this compound is left in the open for some time,it becomes a hard solid mass and cannot be used for moulding purposes. Identify the sulphate salt and explain why it shows such behavior. Provide the chemical reaction involved.

Explain the action of dilute hydrochloric acid on the following with chemical equations:
$(a)$ Magnesium ribbon
$(b)$ Sodium hydroxide
$(c)$ Crushed egg shells

Write true or false for the following statement:
Acids that give rise to more $H^+$ ions are said to be strong acids,and acids that give less $H^+$ ions are said to be weak acids.

What is the concentration of $[H_3O^+]$ in distilled water at $298 \; K$?