Which of the following is a mineral acid?

Acid + Metal oxide $\longrightarrow$ ?

What is meant by $p$ and $H$ in $pH$?

$(a)$ Tooth enamel is one of the hardest substances in our body. Explain the changes in $pH$ of the mouth that indicate tooth decay. How does toothpaste help in preventing it?
$(b)$ What is the nature of the salt if the $pH$ of its solution is greater than $7$? Name the acid and base that would be used to prepare the following salts:
$(i)$ Potassium sulphate.
$(ii)$ Ammonium chloride.

Which of the following substances will not give carbon dioxide on treatment with dilute acid?

Which of the following salts has a $pH$ less than $7$? Why?