How is an aqueous solution with $pH$ $12$ compared to an aqueous solution with $pH$ $9$?

Which of the following solutions will have $pH = 2$?

What is the concentration of $[OH^-]$ in distilled water at $298 \; K$?

In an attempt to demonstrate electrical conductivity through an electrolyte,the following apparatus was set up. Which among the following statement$(s)$ is(are) correct?
$(i)$ Bulb will not glow because electrolyte is not acidic.
$(ii)$ Bulb will glow because $NaOH$ is a strong base and furnishes ions for conduction.
$(iii)$ Bulb will not glow because circuit is incomplete.
$(iv)$ Bulb will not glow because it depends upon the type of electrolytic solution.
Solution: The apparatus shows a beaker containing a dilute $NaOH$ solution with two nails fixed on a rubber cork. $NaOH$ is a strong base that dissociates completely in water to provide $Na^+$ and $OH^-$ ions. These free ions act as charge carriers,allowing the electric current to flow through the solution and complete the circuit. Therefore,the bulb will glow. Statement $(ii)$ is correct.

Which of the following gives the correct increasing order of acidic strength?

State the number of water molecules present in crystals of washing soda and Plaster of Paris. What are these water molecules called?