To determine which salt will give the highest pH in water, we need to consider the nature of the ions produced when each salt dissolves.$\\$1. $$KCl and NaCl are salts of strong acids (HCl) and strong bases (KOH and NaOH, respectively).$\\$• When dissolved in water, they dissociate completely into K$^+$, Na$^+$, and Cl$^-$ ions.$\\$• These ions do not hydrolyze, so the solution remains neutral with a pH around 7.$\\$2. $$CuSO$_4$ is a salt of a weak base (Cu(OH)$_2$) and a strong acid (H$_2$SO$_4$).$\\$• When dissolved, it forms Cu$^{2+}$ and SO$_4^{2-}$ ions.$\\$• The Cu$^{2+}$ ion hydrolyzes in water, producing H$^+$ ions, making the solution acidic with a pH less than 7.$\\$3. $$Na$_2$CO$_3$ is a salt of a strong base (NaOH) and a weak acid (H$_2$CO$_3$).$\\$• When dissolved, it forms 2 Na$^+$ and CO$_3^{2-}$ ions.$\\$• The CO$_3^{2-}$ ion hydrolyzes in water, producing OH$^-$ ions, making the solution basic with a pH greater than 7.$\\$Therefore, the salt that will give the highest pH in water is Na$_2$CO$_3$, as it forms a basic solution.$\\$Thus, the correct option is Option 3: Na$_2$CO$_3$.