Does the pH increase, decrease, or remain the same on the addition of each of the following? (a) NH4NO3 to an NH3 solution (b) Na2CO3 to an NaHCO3 solution (c) NaClO4 to an NaOH solution

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1. Identify the nature of each compound involved in the problem. NH4NO3 is an ammonium salt, NH3 is a weak base, Na2CO3 is a basic salt, NaHCO3 is a weak acid, NaClO4 is a neutral salt, and NaOH is a strong base.
2. For part (a), consider the reaction of NH4NO3 with NH3. NH4NO3 dissociates into NH4+ and NO3-. NH4+ is the conjugate acid of NH3, which can donate a proton to water, slightly increasing the acidity of the solution and thus decreasing the pH.
3. For part (b), consider the addition of Na2CO3 to NaHCO3. Na2CO3 dissociates into 2 Na+ and CO3^2-. CO3^2- is a stronger base than HCO3-, so it will react with water to form OH- ions, increasing the pH of the solution.
4. For part (c), analyze the effect of adding NaClO4 to NaOH. NaClO4 dissociates into Na+ and ClO4-. Both ions are neutral in terms of acid-base chemistry, so they do not affect the pH of the NaOH solution, which remains the same.
5. Summarize the effects: (a) pH decreases due to the acidic nature of NH4+, (b) pH increases due to the basic nature of CO3^2-, and (c) pH remains the same as NaClO4 does not affect the basicity of NaOH.