Answer : The volume of 6M NaOH stock solution is, 16.7 mL
Explanation :
To calculate the volume of NaOH stock solution, we use the equation given by neutralization reaction:

where,
are the molarity and volume of NaOH stock solution.
are the molarity and volume of NaOH.
We are given:

Putting values in above equation, we get:

Thus, the volume of 6M NaOH stock solution is, 16.7 mL
There are approximately 160 grams in 1 mol of Fe2O3 molecules. Therefore, there would be 79/160= 0.49375 mols of Fe2O3 molecules in 79 grams. There are 5 atoms in total for each molecule of Fe2O3, therefore 79/160 * 5 = 79/32 = 2.46875 mols of atoms.