Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Covalent single bonds in biological molecules have energies similar to the energy of the C-C bond in ethane. Reason (R): It is because less electrons are shared between atoms in double bonds they require more energy to break than single bonds. In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A) \
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A) \
• C. (A) is correct but (R) is not correct \
• D. (A) is not correct but (R) is correct

Hint:

More shared electrons mean a stronger bond, shorter bond length, and higher dissociation energy. Double bonds share 4 electrons; single bonds share 2.

Answer 1

The Correct Option is C

Step 1: Concept Chemical bond energy refers to the amount of energy required to break a specific chemical bond between atoms.

Step 2: Meaning Single covalent bonds involve the sharing of one pair of electrons, whereas double bonds involve the sharing of two pairs (more electrons). More shared electrons create a stronger attractive force between nuclei.

Step 3: Analysis * Assertion (A) is correct: Covalent single bonds in common biomolecules (such as C-C, C-O, C-N) share typical bond energies of around 350-400 kJ/mol, which is highly comparable to the C-C bond in ethane. * Reason (R) is incorrect: Double bonds involve sharing more electrons (4 electrons), not fewer, compared to single bonds (2 electrons). This greater electron density requires higher energy to break.

Step 4: Conclusion Since the assertion is true but the reason contains a false chemical statement, option C is correct. Final Answer: (C)