A solution of NaOH(aq) is used to neutralize the acidic solution (part a) in an acid base or metathetical reaction. After the H ion has been neutralized by the base, addition of more base increases the OH concentration.
you can use red litmus to test for the point where the addition of the base is sufficient to give a basic solution. the excess OH ions react with the Cu to form the insoluble light blue hydroxide, Cu(OH)