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. forms acid-rain
• B. is a reducing agent
• C. is soluble in water
• D. is used as a food-preservative

Answer 1

The correct option is D is used as a food-preservative

Nitrogen dioxide and sulphur dioxide are both soluble in water. So, as this solubility in water is shown by both of these oxides, (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:


$S{O}_2+\frac{1}{2}{O}_2+H_{2}O\to H_{2}S{O}_4$

$2N{O}_2+\frac{1}{2}{O}_2+H_{2}O\to 2HN{O}_3$

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.
Option (b) is correct