This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “P-Block Elements – Dinitrogen”.
1. Which of the following compounds can be used to obtain free nitrogen?
Explanation: NaNO2, sodium nitriteis the only convenient compound that can be used to obtain free nitrogen, even in laboratories. Sodium nitrite can be reacted with ammonium chloride, both in aqueous form, producing NaCl and nitrogen, N2 along with water and small traces of HNO3 and NO.
2. How many stable isotopes does the nitrogen atom have?
Explanation: The nitrogen atom has two stable isotopes: 14N and 15N, 99.6% and 0.4% (by mass) respectively. There are also fourteen known radioisotopes with one additional nuclear isomer.
3. Nitrogen atom is represented at 147N. How many electrons does it need to attain the noble gas configuration?
Explanation: With five electrons in its outer most shell, it needs three more electrons to have a complete shell consisting of eight electrons which is the noble electronic configuration. The ion formed by the nitrogen atom is N3-. It attains the electronic configuration on neon.
4. Why does nitrogen show anomalous properties with respect to other elements in group 15?
a) Nitrogen has low ionization enthalpy
b) Nitrogen atomhas high inter-electronic repulsions
c) Nitrogen molecule bears a triple bond
d) Absence of vacant d-orbitals
Explanation: Nitrogen shows anomalous properties compared to other elements of group 15 because of the absence of vacant d-orbitals. In addition to this, anomalous properties are a result of nitrogen atom’s smaller size, highest electronegativity and highest ionization energy with respect to all the elements in group 15.
5. Why is nitrogen preferably used in welding process and cooling of substances?
a) It’s a gas and can easily be handled
b) It has an extremely low freezing point
c) It is an inert gas
d) It is non-toxic
Explanation: Gases like argon is also nontoxic. However, nitrogen gas is still the most preferred since it eliminates all the possibilities of unwanted oxidation and explosions. In the welding industry this prevents metals from corroding. Nitrogen is used in the food industry for packaging since it provides a pressurized atmosphere that reduces package collapse.
6. Which oxide of nitrogen is released from car engines?
a) Nitrogen dioxide
b) Nitric oxide
c) Nitrous oxide
d) Nitrogen tetroxide
Explanation: Car engines release only nitric oxides. Nitrogen and oxygen from the air combine at high temperatures in the engine to produce nitrogen (II) oxide by the reaction N2(g) + O2(g) → 2NO(g). Nitric oxides rise in the atmosphere and are oxidized to nitrogen dioxide, NO2 which dissolves in the precipitating water to form acid rain.
7. What is the name of the natural process that is responsible for replenishing N2 back in the atmosphere from NO3–?
b) Nitrogen fixation
d) Nitrate fixation
Explanation: All the mentioned steps are critical in the nitrogen cycle. However, de-nitrification is that particular step where microbes in the soil reduce nitrate ions, NO3–, to free nitrogen gas, N2. It also releases few nitrogen oxides as by-products.
8. When liquid nitrogen is poured onto the hand, it slips away without affecting the hand actually. What is this phenomenon called?
a) Kaye effect
b) Kinetic isotope effect
c) Kondo effect
d) Leiden frost effect
Explanation: The Leiden frost effect creates a small layer of insulating vapor layer just at the instant when the liquid particle strikes a surface comparatively a lot hotter than liquid. Liquid nitrogen is at -196°C and the human body at 38°C. This insulating vapor layer prevents the liquid to further come in contact with the body which then slips away.
9. Which group does the name ‘pnictogens’ refer to?
a) Group 11
b) Group 13
c) Group 15
d) Group 14
Explanation: The group 15 of periodic table is better known as the ‘pnicogens’. Pnicogen means ‘to choke’. Since all the elements in this group is choking in nature, including the choking property of nitrogen. Group 11 does not have a specific name; group 13 is referred to as the Boron group. Group 14 is known as the Carbon group.
10. How many allotropes does nitrogen have?
Explanation: Nitrogen atom does not exhibit allotropy. This is because of its relatively small size and high inter-electronic repulsion due to which the N – N becomes extremely weak. However, theoretically there are two predicted forms of allotropes of nitrogen. First, alpha nitrogen assumes a cubic structure and exists only below 35.6 K which is a whooping -237.55°C. Beta nitrogen exists from 35.6 K to 63.15 K. After that, it melts.
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