Given below are two statements:
Statement I: Boron is extremely hard indicating its high lattice energy.
Statement II: Boron has the highest melting and boiling point compared to its other group members.
Statement I is incorrect but Statement II is correct
Both Statement I and Statement II are correct
Statement I is correct but Statement II is incorrect
Both Statement I and Statement II are incorrect
Correct answer:A
Standard Method
Given: Two statements about Boron are to be evaluated.
Find: Which option correctly identifies the truth values of Statement I and Statement II.
Statement I: Boron is extremely hard indicating its high lattice energy.
Boron forms a giant covalent structure rather than an ionic lattice. Its hardness is due to its strong covalent network, not high lattice energy. Therefore, Statement I is incorrect.
Statement II: Boron has the highest melting and boiling point compared to its other group members.
Boron has a very high melting and boiling point due to its strong covalent network structure. This is true compared to the other group 13 elements. Therefore, Statement II is correct.
Therefore, Statement I is incorrect but Statement II is correct.
The correct option is A.
Why Statement I Fails
Given: The statements compare the properties of Boron with an explanation for its hardness.
Find: Whether the reason given in Statement I is valid.
A common confusion is to attribute hardness to lattice energy. That idea applies to ionic solids. However, Boron is not described by an ionic lattice here. It has a covalent network structure.
So, the hardness of Boron is explained by strong covalent bonding throughout the structure, not by high lattice energy. Hence, Statement I is incorrect.
Since Boron does have the highest melting and boiling point among its group members, Statement II is correct.
Thus, the correct option remains A.
Mistake: Treating Boron as an ionic solid and using lattice energy to explain its hardness. Why it is wrong: Boron shows a giant covalent network, not an ionic lattice. What to do instead: Relate its hardness to strong covalent bonding in the extended structure.
Mistake: Assuming that all group 13 elements have similar melting and boiling points. Why it is wrong: Boron is structurally very different from the heavier members and has unusually high values. What to do instead: Compare Boron separately because of its network covalent character.
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