Test: Nitrogen and Oxygen Family - Chemistry MCQ

Treating copper chips with concentrated nitric acid releases toxic brown gas, NO₂, nitrogen (IV) oxide. It is a reddish-brown gas with pungent odor.

In the gas state, the nitric acid molecule has a triangular planar shape with a steric number of 3 no lone pairs of electron. There are two major resonance forms of nitric acid.

The brown ring test is used to determine the presence of nitrate ions, NO₃^–. Dilute ferrous sulfate solution is added to solution containing nitrate ion. Following this, concentrated sulfuric acid is added along the sides of the test tube. A brown ring is formed at the junction concentrated sulfuric acid and solutions.

Ammonia is oxidized to nitrogen (II) oxide in the presence of Pt/Rh gauze catalyst at a temperature of 500 K and a pressure of 9 bars. The nitrous oxide is then converted to nitrogen dioxide which is further reacted with water to produce nitric acid. The NO formed is recycled.

Di-nitrogen trioxide is formulated as N₂O₃
The oxidation state of oxygen atom is fixed at -2 since it is the more electronegative atom in this case.
If oxidation state of nitrogen is assumed to be ‘x’, then:
2x + (3x -2) = 0
2x – 6 = 0
x = +3
The oxidation state of nitrogen is +3.

Selenium has eight allotropic forms, of which three are red monoclinic forms containing Se₈ rings. The thermodynamically most stable form is grey hexagonal metallic Selenium which consists of polymeric helical chains.

Oxygen is the most reactive element of group 16. It is the second most electronegative element in the periodic table (EN = 3.5), the first being fluorine (EN = 4.0), making it more reactive than the other elements of the group.

The grey form of Selenium (metallic) and Tellurium consist of parallel chains held by weak metallic bonds. In the presence of light, the weak metallic bonds are excited and as a result, the number of free electrons increases and so does the conductivity. Thus, these elements conduct electricity significantly only in the presence of light. That is why Se and Te are called photosensitive elements.

Oxygen is the most reactive group 16 element. Its reactivity is only slightly less than the most reactive elements, halogens. Sulphur is also very reactive particularly at high temperatures which helps in the cleavage of S-S bonds present in S₈ molecules. However, as we move down the group, the reactivity decreases, i.e., O > S > Se > Te > Po.

The hydride of Oxygen, i.e., H₂O is a colourless, odourless liquid while the hydrides of all the other group 16 elements are unpleasant, foul smelling, poisonous gases. H₂O has the highest boiling point of 373 K amongst the hydrides of group 16 elements.