Na20 → NaHCO3 → Na2C03 → NaOH → NaH,PO, → → NagP04;

It seems like you have provided a chemical reaction sequence involving different sodium compounds. It looks like there may be some missing information and errors in the sequence you have provided.

Let's correct and complete the sequence based on the typical reactions involving sodium compounds:

1. Na2O (sodium oxide) + CO2 (carbon dioxide) + H2O (water) → 2 NaHCO3 (sodium bicarbonate, also known as baking soda)
2. 2 NaHCO3 (sodium bicarbonate) → Na2CO3 (sodium carbonate) + H2O (water) + CO2 (carbon dioxide)
3. Na2CO3 (sodium carbonate) + Ca(OH)2 (calcium hydroxide) → 2 NaOH (sodium hydroxide) + CaCO3 (calcium carbonate)
4. 2 NaOH (sodium hydroxide) + H3PO4 (phosphoric acid) → Na2HPO4 (sodium phosphate) + 2 H2O (water)
5. Na2HPO4 (sodium phosphate) + CaCl2 (calcium chloride) → CaHPO4 (calcium phosphate) + 2 NaCl (sodium chloride)

Please note that this is just one possible reaction sequence involving various sodium compounds. Make sure to verify and study the reactions thoroughly for your university exams.