How is the concentration of hydroxide ions $(OH^-)$ affected when excess base is dissolved in a solution of sodium hydroxide?

Fresh milk has a $pH$ of $6$. How do you think the $pH$ will change as it turns into curd? Explain your answer.

Do basic solutions also have $H^+_{(aq)}$ ions? If yes,then why are these basic?

Plaster of Paris should be stored in a moisture-proof container. Explain why?

Write word equations and then balanced chemical equations for the reactions taking place when:
$(a)$ Dilute sulphuric acid reacts with aluminium powder.
$(b)$ Dilute hydrochloric acid reacts with iron filings.

What will happen if a solution of sodium hydrogencarbonate is heated? Give the equation of the reaction involved.