Assertion : Sigma ( $\sigma$ is a strong bond, while pi $(\pi)$ is a weak bond. Reason : Atoms rotate freely about pi ( $\pi$ ) bond.

• A

  If both the assertion and reason are true and reason is a correct explanation of the assertion.
• B

  If both assertion and reason are true but assertion is not a correct explanation of the assertion.
• Correct answer
  C

  If the assertion is true but the reason is false.
• D

  If both assertion and reason are false.

Solution

Sigma bonding involves end to end overlapping of the two atomic orbitals e.g. between $s$ and $s, s$ and $p$ and $p$ and $p$ orbitals. Pi bonding $(\pi)$ involves sidewise overlapping of the two atomic orbitals e.g. between $p$ and $p$ orbitals. Overlapping of orbitals is more effective in $\sigma$ bonding than in $\pi$-bonding. Due to the geometry of overlapping or orbitals, rotation of one atom is not
possible around $\pi$-bonds.

Hence, the correct answer is option: 'C'.