Which of the following is a weak acid?

What is the $pH$ value for a neutral aqueous solution?

What is the $pOH$ value of a $10^{-4} \; M$ aqueous solution of $HCl$?

Three acidic solutions $A, B$ and $C$ have $pH = 0, 3$ and $5$ respectively.
$(i)$ Which solution has the highest concentration of $H^{+}$ ions?
$(ii)$ Which solution has the lowest concentration of $H^{+}$ ions?

State whether the following statement is true or false:
When the $pH$ of rainwater is more than $5.6,$ it is called acid rain.

Tooth enamel is the hardest substance in our body. Name the compound of which it is made up. At what $pH$ of the mouth does it get corroded? State the role of bacteria present in the mouth. Suggest a method to prevent tooth decay.