JEE Main 2023 · 12 April · morning · Single correct · +4 / −1
Given below are two statements :
Statement I : Boron is extremely hard indicating its high lattice energy.
Statement II : Boron has highest melting and boiling point compared to its other group members.
In the light of the above statements, choose the most appropriate answer from the options given below :
- (a) Both Statement I and Statement II are incorrect
- (b) Statement I is incorrect but Statement II is correct
- (c) Statement I is correct but Statement II is incorrect
- (d) Both statement I and Statement II are correct
Answer and solution
Answer (d) Both statement I and Statement II are correct
Solution
Chemistry ma’am · 3 steps
Boron's strong, tightly bonded crystal lattice explains both its hardness and its record melting point.
- Why boron is hard. Boron is a non-metal. Its atoms join into B₁₂ icosahedra, and these units link to one another by strong covalent bonds into a giant three-dimensional network. Breaking or deforming this lattice needs a lot of energy, so boron is extremely hard. Statement I is correct.
- Same lattice, high melting. To melt or boil boron, many strong covalent bonds must break. The other members are metals held by weaker metallic bonding, so they melt and boil at much lower temperatures.
Element Melting point Boiling point B 2453 K 3923 K Al 933 K 2740 K Ga 303 K 2676 K In 430 K 2353 K Tl 576 K 1730 K - So. Boron has the highest melting and boiling points in group 13, so Statement II is correct too. Both statements are correct, which is option (d).
The idea to keep. In group 13, boron is the odd one out: a covalent network solid among metals. That one fact explains its hardness and its very high melting and boiling points.
Answer from the NTA final answer key. Solution by PrepWiser.