Given data:
- Mass of As2O3 sample = 0.46 g
- Volume of KmnO4 solution used = 25.0 mL

Calculating the molarity of KmnO4 solution:

Step 1: Convert the volume of KmnO4 solution from mL to L:
- 25.0 mL = 25.0 mL * (1 L/1000 mL) = 0.025 L

Step 2: Calculate the number of moles of As2O3:
- The molar mass of As2O3 = 2 * atomic mass of As + 3 * atomic mass of O
- The atomic mass of As = 74.92 g/mol
- The atomic mass of O = 16.00 g/mol
- The molar mass of As2O3 = 2 * 74.92 g/mol + 3 * 16.00 g/mol = 197.84 g/mol
- Number of moles of As2O3 = mass of As2O3 / molar mass of As2O3
- Number of moles of As2O3 = 0.46 g / 197.84 g/mol = 0.00232 mol

Step 3: Determine the stoichiometry between As2O3 and KmnO4:
- The balanced equation for the reaction between As2O3 and KmnO4 is:
2 As2O3 + 10 KmnO4 + 8 H2SO4 → 4 H3AsO4 + 5 K2SO4 + 10 MnSO4 + 8 H2O
- From the balanced equation, we can see that 1 mole of As2O3 reacts with 5 moles of KmnO4.

Step 4: Calculate the number of moles of KmnO4:
- Number of moles of KmnO4 = (number of moles of As2O3) * (5 moles of KmnO4 / 1 mole of As2O3)
- Number of moles of KmnO4 = 0.00232 mol * (5 mol/1 mol) = 0.0116 mol

Step 5: Calculate the molarity of KmnO4 solution:
- Molarity (M) = moles of solute / volume of solution in liters
- Molarity of KmnO4 solution = 0.0116 mol / 0.025 L = 0.464 M

Answer:
The molarity of the KmnO4 solution is 0.464 M.