If the $pH$ of an aqueous solution is $6$,then its $pOH$ is:

Explain why:
$(a)$ the colour of copper sulphate crystals changes on heating?
$(b)$ baking soda acts as an antacid?
$(c)$ an acid should be added to water while diluting?

Give reasons for the following:
$(a)$ Aqueous solution of an acid conducts electricity.

$A$ sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the $pH$ paper yellowish-orange. Which of the following would change the colour of this $pH$ paper to greenish-blue?

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

Acid and base react with each other and form salt and water. What is this reaction called in scientific language?