Question

Carbon dioxide and sulphur dioxide gas can be distinguished by using :

• A. moist blue litmus paper
• B. lime water
• C. acidified potassium dichromate paper
• D. none of the above

Answer 1

The correct option is C acidified potassium dichromate paper

If sulfur dioxide gas is bubbled through acidified potassium dichromate solution, the orange solution turns green, indicating that $C{r}_2{O}_7^{2-}$ has been reduced to $C{r}^{3+}$.
$C{r}_2{O}_7^{2-}+2H^{+}+3S{O}_2\to 2C{r}^{3+}+H_{2}O+3S{O}_4^{2-}$
But $C{O}_2$ doesn't give this test as it cannot oxidise further, so it can not reduce dichromate solution.