 We start out with a light green solution of nickel sulfate. We're going to add to it a closed solution of sodium chloride. When they add the sodium chloride to the nickel sulfate, we see that there's no precipitate formed. The sodium chloride and the nickel sulfate are water soluble. The potential products nickel chloride and sodium sulfate are also soluble. What we end up with is a solution that contains nickel ions, chloride ions, sodium ions, and sulfate ions in aqueous solution. No precipitate is formed, no reaction occurs.