In the iodometric estimation in the laboratory which process is involved?

Options

A. `Cr_(2)O_(7)^(2-)+H^(+)+I^(-)rarr2Cr^(3+)+I_(2),I_(2)+S_(2)O_(3)^(2-)rarrS_(4)O_(6)^(2-)+I^(-)`
B. `MnO_(4)^(2-)+H^(+)+I^(-)rarrMn^(2+)+I_(2),I_(2)+S_(2)O_(3)^(2-)rarrS_(4)O_(6)^(2-)+I^(-)`
C. `MnO_(4)^(-)+OH^(-)+I^(-)rarrMnO_(2)+I_(2),I_(2)+S_(2)O_(3)^(2-)rarrS_(4)O_(6)^(2-)+I^(-)`
D. `Cr_(2)O_(7)^(2-)+OH^(-)+I^(-)rarr2Cr^(3+)+I_(2),I_(2)+S_(2)O_(3)^(2-)rarrS_(4)O_(6)^(2-)+I^(-)`

Answer

A

Explanation

Iodometry involves oxidation of iodide ion (usually KI) by strong oxidising agent in neutral or acidic solution to `I_(2)`. The `I_(2)` evolved is then titrated with standard solution of a reducing agent (generally `Na_(2)S_(2)O_(3)`). In choices (C), and (D), medium is alkaline and in choice (B), `MnO_(4)^(2-)` (mangnate) is not a strong oxidising agent.