This collection of multiple-choice questions (MCQs) for BPSC PGT Chemistry is centered on “p-Block Elements.” Covering a wide range of p-Block Elements Important Questions, these MCQs are designed according to the latest CBSE syllabus and the NCERT curriculum, providing essential support for exam preparation.
- The atomic radius of gallium is greater than that of aluminum.
a) True
b) False
Answer: (b)
Explanation:
Although atomic radii increase as you move down the group, the radius of gallium decreases unexpectedly. This is due to the presence of electrons in orbitals that do not effectively shield the nucleus’s attraction. As a result, the atomic radius of gallium is smaller than that of aluminum.
- 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 atoms react with six moles of sodium hydroxide (NaOH) to form two moles of sodium borate (Na₃BO₃) and three moles of hydrogen gas (H₂). Sodium hydroxide is commonly known as caustic soda.
- 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 in the solid state, making its structure weak and easy to break. However, it remains in the liquid state up to 2276 K, making it suitable for use in high-temperature thermometers. Gallium’s chemical symbol is Ga, and its atomic number is 31.
- 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, ionization enthalpy generally decreases from boron to aluminum. However, gallium has a slightly higher ionization enthalpy than aluminum due to the poor shielding effect of intervening d-electrons. The trend then shows a slight increase in indium, followed by a decrease in thallium.
- Inert pair effect __________ down the group.
a) Increases
b) Decreases
c) Constant
d) Is a regular
Answer: (a)
Explanation: The inert pair effect refers to the reluctance of valence shell s-electrons (ns²) to participate in bonding. This occurs due to poor shielding by intervening d- and f-electrons. As we move down the group, the inert pair effect becomes more prominent, leading to lower oxidation states in the heavier elements of the group.
- 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 occupies the outermost p-orbital. Elements from group 13 to group 18 are all part of the p-block. Group 13 is known as the boron family, which includes the elements boron, aluminum, gallium, indium, and thallium.
- Which of the following elements exhibits + 3 Oxidation State only?
a) Gallium
b) Thallium
c) Indium
d) Aluminium
Answer: (d)
Explanation: Boron and aluminum exhibit only a +3 oxidation state, whereas gallium, indium, and thallium can show both +1 and +3 oxidation states. As we move down the group, the tendency to exhibit the +3 oxidation state decreases due to the increasing inert pair effect.
- 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 character of the boron family decreases down the group from aluminum to thallium due to the increasing electrode potential value for M³⁺/M. As a result, the correct order of reducing strength is:
Aluminum > Gallium > Indium > Thallium.
- 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: The boron family shows a higher tendency for complex formation compared to s-block elements due to their smaller atomic size and higher charge density. This makes them more likely to form complexes than alkali and alkaline earth metals.
- The compounds formed by the Boron family are __________
a) ionic
b) covalent
c) both ionic and covalent
d) neither ionic nor covalent
Answer: (c)
Explanation: The tendency to form ionic compounds increases from boron to thallium. Boron forms only covalent compounds, while aluminum can form both covalent and ionic compounds. As we move further down the group, gallium and the heavier elements predominantly form ionic compounds.
- Which of the following groups’ 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: The atomic and ionic radii of Group 13 elements are smaller than those of alkali and alkaline earth metals, primarily due to the higher effective nuclear charge. As you move down the group, the atomic radii increase, although an anomaly is observed at gallium.
- What is the chemical formula of aluminium carbide?
a) AlC
b) AlC3
c) AlC2
d) AC3
Answer: (b)
Explanation: When 4 moles of aluminum atoms react with 3 moles of carbon atoms upon heating, they form aluminum carbide (Al₄C₃). Aluminum carbide is ionic in nature and reacts with water to produce methane (CH₄). Its correct chemical formula is Al₄C₃.
- 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: Upon heating, two moles of boron atoms react with one mole of nitrogen molecules to form two moles of boron nitride (BN). Similarly, aluminum reacts with nitrogen in the same manner to form aluminum nitride (AlN).
- 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 alkaline earth metals due to their smaller atomic size and higher ionization enthalpies. As we move down the group, electropositivity initially increases from boron to aluminum but then decreases from gallium to thallium due to the poor shielding effect of d- and f-orbitals.
- Which of the following is the correct order for the stability of a plus one oxidation State?
a) Ga < In < Tl
b) Ga < In > Tl
c) Ga > In < Tl
d) Ga > In > Tl
Answer: (a)
Explanation: The stability of the +1 oxidation state increases as we move down the group in the boron family. The correct order of increasing stability is:
Gallium < Indium < Thallium.
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