Question

Assertion (A): Carbon can form $p\pi - p\pi$ bonds with itself and with other small sized and highly electronegative atoms.
Reason (R): Other heavier elements of group 14 can also form $p\pi - p\pi$ bonds.
Choose the correct option:

• 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
• D. (A) is not correct but (R) is correct

Hint:

$p\pi - p\pi$ multiple bonding is strongest for carbon due to its small size and good p orbital overlap; heavier elements rarely form stable multiple bonds.

Answer 1

The Correct Option is C

Step 1: Start from the general rule about $p\pi$-$p\pi$ overlap, before touching carbon specifically.
Two atoms can form a strong $p\pi$-$p\pi$ bond only when their p orbitals are close in size and energy, which happens for small, second-period atoms like C, N, and O. Once atoms get bigger, their p orbitals become larger and more diffuse, and side-on overlap becomes too weak to hold a stable multiple bond.

Step 2: Apply this rule to carbon, which is what Assertion (A) claims.
Carbon is small and sits in the second period, so it satisfies the size and energy-matching condition. It readily forms $p\pi$-$p\pi$ bonds with itself, as in $C=C$ and $C \equiv C$, and with other small electronegative atoms like N and O, as in $C=N$ or $C=O$. Assertion (A) fits the general rule, so it is correct.

Step 3: Apply the same rule to the heavier group 14 elements, which is what Reason (R) claims.
Silicon, germanium, and tin lie in the third period and below, so their p orbitals are much larger and more diffuse than carbon's. Side-on overlap between such large orbitals is too weak to support a genuine $p\pi$-$p\pi$ bond, which is exactly why compounds like $Si=Si$ are unstable or need special stabilisation. Reason (R) goes directly against the general rule, so it is false.

Step 4: Decide the relationship between A and R.
Since R is factually wrong, it cannot explain A, whether or not A itself is true.

Final Answer:
\[ \boxed{\text{(A) is correct but (R) is not}} \]