Which aqueous solution has highest pH?

0.1 MNH4CL

0.1 M ( N H 4 ) 2 S O 4

0.1 M CH3COONa

0.1M Na₂CO₃

Na₂CO₃ is the salt that will produce the highest pH when dissolved in water because it is derived from a strong base (NaOH) and a weak acid (H₂CO₃).