Class 12 Chemistry MCQ – P-Block Elements – Dioxygen

This set of Class 12 Chemistry Chapter 7 Multiple Choice Questions & Answers (MCQs) focuses on “P-Block Elements – Dioxygen”.

1. Which of the following is the most abundant non-metal in the Earth’s crust?
a) Oxygen
b) Silicon
c) Hydrogen
d) Water
View Answer

Answer: a
Explanation: Oxygen constitutes about 46-47% of the Earth’s crust, followed by Silicon at 27-28%. Oxygen is predominantly present as a gas in air and several metallic compounds that constitute a metal ore (in the form of oxides). Apart from these, Aluminum is the most abundant metal in the Earth’s crust followed by Iron.

2. What is the source of obtaining oxygen industrially?
a) Metallic ores
b) Air
c) Oxygen furnace
d) Organic compounds
View Answer

Answer: b
Explanation: Industrially, oxygen is isolated by implying the technique of fractional distillation of liquefied air. Prior to the main operation, air is cleared and filtered off to remove impurities such as carbon dioxide and water vapor. Oxygen distills off as a liquid at -183°C.

3. What is the most stable oxidation state of the oxygen atom?
a) +1
b) -1
c) -2
d) +2
View Answer

Answer: c
Explanation: Oxygen atom is the most stable in its -2 oxidation state. Here, it gains 2e to complete its octet and obtain the noble gas configuration of [Ne]. Rarely does oxygen show +1 and -1 oxidation states. The -1 state is displayed in peroxides. E.g. H2O2. It shows +1 in oxygen (I) fluoride, OF2.

4. Why does aluminum not degrade in nature quickly?
a) It reacts at low temperature
b) It has an octet configuration
c) It has a tough oxide layer
d) It is an electronegative element
View Answer

Answer: c
Explanation: Aluminum is a passive metal. Meaning, when formed in nature, it quickly reacts with oxygen in the air to form a tough, non-corrosive oxide layer. This layer prevents aluminum metal from reacting with any other substance.

5. Marine life is more comfortable in warm water than cold water. True or false?
a) True
b) False
View Answer

Answer: b
Explanation: The solubility of gases in a liquid is governed by Henry’s law. It states that the partial pressure of a gas in a solution varies directly. In warmer conditions, the gas particles tend to escape from the water body leading to a lesser amount of dissolved oxygen required for comfortable aquatic conditions.
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6. Which of the following in air, forms compounds readily?
a) Nitrogen
b) Oxygen
c) Sulfur
d) Carbon
View Answer

Answer: b
Explanation: Oxygen, being a highly electronegative element and reactive tends to react with several substances. These include hydrogen and different occurring metals which form compounds. E.g. iron, magnesium, calcium. Nitrogen is highly unreactive since it bears a triple bond and reacts only at high temperatures. Carbon and sulfur are not elements present in air since they are not gases.

7. What will be the products of the reaction – C2H4 + 2O2 →?
a) CO and H2O
b) CO2 and H2O2
c) Co and H2O
d) CO2 and H2O
View Answer

Answer: d
Explanation: The reaction show depicts the combustion of ethane. When a hydrocarbon is burned in excess oxygen it forms carbon dioxide and water. Co represents cobalt and CO represents carbon monoxide.

8. What is the nature of zinc oxide?
a) Acidic
b) Amphoteric
c) Basic
d) Undetermined
View Answer

Answer: b
Explanation: Amphoteric oxides are those oxides which can act both as an acid as well as base. Factually it is determined that zinc, aluminum and tin oxides are amphoteric in nature.

9. Which is the most electronegative atom amongst the following?
a) Oxygen
b) Fluorine
c) Nitrogen
d) Chlorine
View Answer

Answer: b
Explanation: Accounting for only one missing electron, fluorine is highly reactive. Since it needs only one electron to complete its octet, it is the most electronegative element in the periodic table. The decreasing order of electronegativity is F > Cl > O > N.

10. What happens when an atom of oxygen is subjected to external magnetic field?
a) It is weakly attracted and loses magnetism on removal of field
b) It is weakly attracted and does not lose magnetism on removal of field
c) It is weakly attracted and domains align themselves in the direction of field
d) It is not attracted
View Answer

Answer: a
Explanation: Oxygen atom is paramagnetic in nature. Meaning, on the application of an external magnetic field, it is slight attracted and loses magnetism on the removal of the field.

Sanfoundry Global Education & Learning Series – Chemistry – Class 12.

To practice all chapters and topics of class 12 Chemistry, here is complete set of 1000+ Multiple Choice Questions and Answers.

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