Question

Nitrogen dioxide and sulphur dioxide have some properties in common. Which property is shown by one of these compounds, but not by another?
(A) is soluble in water
(B) is used as a food-preservative
(C) forms acid-rain
(D) is a reducing agent

Answer 1

Hint: Nitrogen and sulphur both atoms in their oxides have high oxidation states. So, it cannot get further oxidized to higher oxidation states. Acid rain occurs when some gases in the atmosphere react with moisture to form inorganic acids.

Complete step by step answer:
Let’s check all the given properties for sulphur dioxide and nitrogen dioxide.
- Nitrogen dioxide and sulphur dioxide are both soluble in water. So, as this solubility in water is shown by both of these oxides, we can say that (A) cannot be a correct answer.
- Sulphur dioxide has an antioxidant property. So, it is used as a food preservative. Preservatives are the compounds that are added in the food in order to decrease the rate of decomposition or degradation of food. Actually sulphur dioxide is a toxic gas and is never found in food but it is found in the form of various salts of sulfurous acid. Nitrogen dioxide is not used as a food preservative.
- Both nitrogen dioxide and sulphur dioxide combine with moisture in the atmosphere to form acids and that causes acid rain. Nitrogen dioxide forms nitric acid and sulphur dioxide forms sulphuric acid in reaction with water. The reaction is given as:

\[S{{O}_{2}}+\dfrac{1}{2}{{O}_{2}}+{{H}_{2}}O\to {{H}_{2}}S{{O}_{4}}\]
     \[2N{{O}_{2}}+\dfrac{1}{2}{{O}_{2}}+{{H}_{2}}O\to 2HN{{O}_{3}}\]

Thus, we can say that both gases form acid rain. Thus, option (C) is also not correct.
- In sulphur dioxide, sulphur is in +4 oxidation state and in nitrogen dioxide, nitrogen is in +4 oxidation state as well. So, as they are in a higher oxidation state already, neither of them have the ability to reduce other compounds. So, neither of them is used as a reducing agent. Thus, option (D) is also not a correct answer. Thus, form above discussion,
So, the correct answer is “Option B”.

Note: The use of sulphur dioxide is not decreasing because it has been found that vitamin B1 (Thiamine) is destroyed by its reaction with sulphites. As a result sulphites cannot be used as a preservative in foods that contain high amounts of Thiamine. e.g. Meat products.