`H_(2)O_(2)` is an unstable liquid . On standing or on heating it decomposes to `H_(2)O` and `O_(2) . H_(2)O_(2)` can acts as oxidising agent and reducing agent . The concentration of `H_(2)O_(2)` is expressed differently with volume strength and the concentration of `H_(2)O_(2)` at a particular time is measured by titrating it with acidified `KMnO_(4)` or by titrating liberated `I_(2)` from acidified KI and `H_(2)O_(2)` with hypo solution . A sample of `H_(2)O_(2)` has 3.4 g of `H_(2)O_(2)` in 100 mL solution . The bottle containing this sample was kept at `25^(0)C` for 15 days then 20mL of this sample is treated with excess KI and the liberated iodine requires 50 mL , 0.2 M `Na_(2)S_(2)O_(3)` solution . Assume the volume of solution remains unchanged . The volume of `H_(2)O_(2)` sample (after 15 days ) that is required to reduce 40 mL of `0.2` M acidified `KMnO_(4)` solution is :A. 40 mLB. 200 mLC. 80 mLD. 100 mL