Which of the following are present in a dilute aqueous solution of hydrochloric acid?

State the chemical property in each of the following cases,on which the following uses of baking soda are based:
$(a)$ Applied on an ant stung area.
$(b)$ As a constituent of baking powder.
$(c)$ In soda-acid fire extinguisher.

What will be the value of $pH$ if blue litmus paper turns red in an aqueous solution?

$(a)$ 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 is not an oxide of metal?

$(a)$ $A$ solution of a substance $'X'$ is used for testing carbon dioxide. Write the equation of the reaction of $'X'$ with carbon dioxide.
$(b)$ How is $'X'$ obtained? Write the chemical equation.