Question

Anion which gives a turning acidified potassium dichromate paper green is:
A.Carbonate
B.Sulphite
C.Sulphate
D.Bromide

Answer 1

Hint:Potassium dichromate is a strong oxidising agent. It is used to convert alcohols into aldehydes and carboxylic acids.
-Anions are electron rich species and have net negative charge.

Complete step by step answer:
Potassium dichromate ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ is defined as an inorganic compound which acts as a strong oxidising agent. It is very harmful for health causing redness and pain. It is a red orange colour compound and it is present in ionic crystalline form. The salt is deliquescent.
Sulphur dioxide is a toxic gas and releases pungent smell. It is soluble in water. It is produced in air due to the burning of coal and as a by-product during the extraction of copper.
The sulfite ion is a weak base and in acidic solution, it converts into sulfurous acid that releases sulphur dioxide gas.
When a sodium dioxide reacts with potassium dichromate it will give chromium sulphate, water and potassium sulphate as a by-product .
Then,
$S{{O}_{2}}+{{K}_{2}}C{{r}_{2}}{{O}_{7}}\to C{{r}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}+{{K}_{2}}S{{O}_{4}}+{{H}_{2}}O$
The sulphur dioxide changes the potassium dichromate paper green and reduces $C{{r}_{2}}{{O}_{7}}^{2}$ to $C{{r}^{3+}}$
Therefore, the correct option is B that is sulphite .

Additional information
Potassium dichromate is highly corrosive and is a strong oxidising agent in acidic medium. Potassium dichromate is a potassium salt . It is the dipotassium salt of dichromic acid. It is used for the oxidation of primary alcohols and secondary alcohols.

Note:
The orange solution of acidified potassium dichromate turns green when sulphur dioxide is passed to the potassium dichromate. In acidic medium sulphite ion is converted into sulfurous acid that releases sulphur dioxide gas. Here, the sulfite ion acts as a reducing agent.