What happens when metal oxide reacts with water?

What type of substance is $NaOH$?

If the approximate $pH$ of a solution is $7,$ what will be the colour of $pH$ paper when dipped into that solution?

Which ions are responsible for the chemical properties of bases in their aqueous solution?

Which of the following statements is true for acids?

Crystals of copper sulphate are heated in a test tube for some time.
$(a)$ What is the colour of copper sulphate crystals:
$(i)$ before heating, and $(ii)$ after heating?