In which case pH will not change on dilution

Mixture of sodium acetate and acetic acid is a buffer of pH value equal to pKa so its buffer capacity is very high and hence its pH will not change significantly while CH3COONH4 is a salt of weak acid CH3COOH and weak base NH4OH whose magnitude of Ka and Kb are equal. So its pH does not depend upon concentration. Furthermore, NaH4PO4 is, in fact, a single solute buffer.