ANSWER
The mass of Na2SO4 is 874g
Step-by-step explanation
Given that;
The number of moles of HCl is 12.3 mol
Follow the steps below to find the mass of sodium sulfate produced
Step 1; Write a balanced equation for the reaction

In the reaction above, 2 moles of NaCl react with 1 mole of H2SO4 to give 2 moles of HCl and 1 mole of Na2SO4
Let the number of moles of Na2SO4 be x

The number of moles of Na2SO4 is 6.15 moles
Step 3; Find the mass of Na2SO4 using the below formula

Recall, that the molar mass of Na2SO4 is 142.04 g/mol

Therefore, the mass of Na2SO4 is 874g