Final answer:
Assuming a 1:1 stoichiometry between Na2S2O3 and Cl2, 0.12 moles of Cl2 would need 0.12 moles of Na2S2O3 to react completely.
Step-by-step explanation:
To determine the number of moles of Na2S2O3 that react with 0.12 mol of Cl2, we need the balanced chemical equation for the reaction. The balanced equation isn't fully provided in the question, but assuming it is a typical reaction where thiosulfate (Na2S2O3) acts as a reducing agent for chlorine, the stoichiometry would look something like this:
Na2S2O3 + Cl2 → 2NaCl + S2O32- (Simplified reaction for demonstration)
In this simplified reaction, we can see that 1 mole of Na2S2O3 reacts with 1 mole of Cl2. Therefore, to react with 0.12 mol of Cl2, we would need 0.12 mol of Na2S2O3.