This set of Multiple Choice Questions & Answers (MCQs) focuses on “p-Block Elements”. These MCQs are created based on the latest CBSE syllabus and the NCERT curriculum, offering valuable assistance for exam preparation.
- Which of the following element exhibits + 3 Oxidation State only?
a) Gallium
b) Thallium
c) Indium
d) Aluminium
Answer: d
Explanation: While boron and aluminium display only the +3 oxidation state, gallium, indium, and thallium can exhibit both +1 and +3 oxidation states. The stability of the +3 state decreases down the group because of the inert pair effect, making the +1 oxidation state more prominent in heavier elements.
- Complex formation is more likely to be possible in __________
a) alkali metals
b) alkaline earth metals
c) boron family
d) equally likely
Answer: c
Explanation: Elements of the boron family tend to form complexes more readily than S-block elements. This is because they have a smaller atomic size and a higher charge, which enhances their ability to attract and bond with ligands making complex formation more likely compared to alkali and alkaline earth metals.
- Which of the following is true regarding reducing character?
a) Gallium < aluminium > indium > thallium
b) Aluminium > gallium > indium > thallium
c) Aluminium > gallium < indium > thallium
d) Gallium > aluminium > indium > thallium
Answer: b
Explanation: The reducing nature of elements in the boron family diminishes from aluminium to thallium as we move down the group. This is due to the rising electrode potential values for the M³⁺/M pair. Hence, the correct decreasing order of reducing character is: aluminium > gallium > indium > thallium.
- Are group 13 elements a part of p block elements?
a) Yes
b) No
c) Only a few
d) Only one
Answer: a
Explanation: In p-block elements, the last electron enters the outermost p-orbital. Groups 13 to 18 are entirely composed of p-block elements. Group 13, specifically known as the boron family, consists of the elements boron, aluminium, gallium, indium, and thallium.
- Gallium remains liquid up to __________ Kelvin.
a) 2176
b) 2376
c) 2476
d) 2276
Answer: d
Explanation: Gallium has a low melting point because it exists as Ga₂ molecules. Interestingly, it remains in the liquid state up to 2276 K, which makes it suitable for use in high-tem perature thermometers. The chemical symbol for gallium is Ga, and its atomic number is 31.
- Inert pair affect __________ down the group.
a) Increases
b) Decreases
c) Constant
d) Is a regular
Answer: d
Explanation: Boron and aluminium exclusively exhibit the +3 oxidation state, whereas gallium, indium, and thallium can show both +1 and +3 oxidation states. As we move down the group, the likelihood of showing the +3 oxidation state decreases. This trend is attributed to the inert pair effect.
- Which of the following group’s elements have smaller atomic radii?
a) Group 1 elements
b) Group 2 elements
c) Group 13 elements
d) All have the same atomic radii
Answer: c
Explanation: Group 13 elements possess smaller atomic and ionic radii compared to alkali and alkaline earth metals because of their higher effective nuclear charge. As we move down the group, the atomic radii generally increase; however, gallium shows an irregularity in this trend.
- The atomic radius of gallium is greater than that of aluminum.
a) True
b) False
Answer: b
Explanation: Although atomic radius generally increase down a group, gallium shows an unexpected decrease in size. This is due to the presence of electrons in inner orbitals that provide poor shielding, allowing the nucleus to exert a stronger pull on the outer electrons. As a result, gallium has a smaller atomic radius than aluminium.
- The ionization enthalpy _________ down the group in the family.
a) Increases
b) Decreases
c) Constant
d) Is a regular
Answer: d
Explanation: As we move down the group from boron to aluminium, the ionization enthalpy decreases. However, gallium shows a slightly higher ionization enthalpy than aluminium because of the poor shielding effect of the intervening d-electrons. Following this, ionization enthalpy increases in indium and then decreases again in thallium.
- Which of the following is the correct order for the stability of plus one Oxidation State?
a) Ga < In < Tl
b) Ga < In > Tl
c) Ga > In < Tl
d) Ga > In > Tl
Answer: a
Explanation: The correct order of increasing stability of the +1 oxidation state among gallium, indium, and thallium is: gallium < indium < thallium. This means that the +1 oxidation state is least stable in gallium, more stable in indium, and most stable in thallium.
- What forms when boron combines with caustic soda?
a) Formation of oxygen
b) Formation of washing soda
c) Formation of Boron nitride
d) Formation of sodium borate
Answer: d
Explanation: Two moles of boron react with six moles of sodium hydroxide (commonly known as caustic soda) to produce two moles of sodium borate and three moles of hydrogen gas.
- The metallic character of __________ is less than that of alkaline earth metals.
a) Boron family
b) Alkali metals
c) Magnesium
d) Hydrogen
Answer: a
Explanation: The elements of the Boron family are less electropositive than the alkaline earth metals due to their smaller size and higher ionization enthalpies. On moving down the group, the electropositive character first increases from Boron to aluminium and then decreases from gallium so thallium due to the presence of d and f orbitals which causes poor shielding.
- What is the chemical formula of aluminium carbide?
a) AlC
b) AlC3
c) AlC2
d) AC3
Answer: b
Explanation: Upon heating, 4 moles of aluminium atoms react with 3 moles of carbon atoms to produce aluminium carbide. This compound is ionic in nature and reacts with water to release methane gas. The chemical formula of aluminium carbide is AlC₃.
- When boron reacts with nitrogen which of the following compound is formed?
a) Boron oxide
b) Boron nitrate
c) Boron hydrides
d) Boron nitride
Answer: d
Explanation: When heated, two moles of boron atoms react with one mole of nitrogen molecules to produce two moles of boron nitride. Similarly, aluminium also reacts with nitrogen upon heating to form aluminium nitride in a comparable manner.
- What forms when boron combines with caustic soda?
a) Formation of oxygen
b) Formation of washing soda
c) Formation of Boron nitride
d) Formation of sodium borate
Answer: d
Explanation: Two moles of boron react with six moles of sodium hydroxide (also known as caustic soda) to produce two moles of sodium borate and three moles of hydrogen gas.