How is an aqueous solution with $pH = 2$ compared to an aqueous solution with $pH = 4$?

Write true or false for the following statement:
Mixing an acid or base with water results in an increase in the concentration of ions $(H_{3}O^{+} / OH^{-})$ per unit volume.

Which of the following is an oxide of metal?

Which metal does not react with acid?

What is the molarity of a solution prepared by dissolving $8 \ g$ of $NaOH$ in water to make a total volume of $100 \ mL$ (in $M$)?

An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change?