Question

what pH should we expect when we add 0.1 molar NaOH to water and why?

Answer 1

NaOH is a strong base. When it is added to water which is neutral, we can expect an alkaline medium ie ph>7.

Answer 2

Without knowing the initial volumes of water and sodium hydroxide, we can't go any farther to determine the pH after mixing, other than indicating that we will have an alkaline solution with a pH > 7.