To solve this problem, we need to analyze the flocculating power of ions and salts in the coagulation of sols.$\\$Statement I: In the coagulation of a negative sol, the flocculating power of the three given ions is in the order $Al^{3+} > Ba^{2+} > Na^+. \\$• According to the Hardy-Schulze rule, the flocculating power of an ion is directly proportional to the valency of the ion.$\\$• For a negative sol, the coagulating ions are cations. The higher the charge on the cation, the greater its flocculating power.$\\$• Therefore, the order of flocculating power should be $Al^{3+} > Ba^{2+} > Na^+$, which is correct.$\\$Statement II: In the coagulation of a positive sol, the flocculating power of the three given salts is in the order $NaCl > Na_2SO_4 > Na_3PO_4. \\$• For a positive sol, the coagulating ions are anions. The higher the charge on the anion, the greater its flocculating power.$\\$• The flocculating power of the anions should be in the order of increasing charge: $Cl^- < SO_4^{2-} < PO_4^{3-}. \\$• Therefore, the correct order should be $Na_3PO_4 > Na_2SO_4 > NaCl$, which contradicts Statement II.$\\$Conclusion:$\\$• Statement I is correct as it follows the Hardy-Schulze rule for negative sols.$\\$• Statement II is incorrect as it does not follow the correct order of flocculating power for positive sols.$\\$Therefore, the correct answer is Option 3: Statement I is correct, but Statement II is incorrect.