Concept involved

The ability to form $p\pi$-$p\pi$ multiple bonds depends mainly on:

• small atomic size,
• effective sideways overlap of unhybridized $p$ orbitals.

Trend in group 14

The given elements are all from group 14:

• $\mathrm{C}$
• $\mathrm{Si}$
• $\mathrm{Ge}$
• $\mathrm{Sn}$

As we move down the group, atomic size increases, so the sideways overlap between $p$ orbitals becomes poorer.

Comparison of the given elements

• Carbon ($\mathrm{C}$) is very small in size, so its $2p$ orbitals overlap effectively.
• Silicon, germanium, and tin are larger atoms with $3p$, $4p$, and $5p$ orbitals respectively, which overlap less effectively for forming strong $p\pi$-$p\pi$ bonds.

Therefore, carbon has the greatest tendency to form multiple bonds such as: $\mathrm{C=C}, \quad \mathrm{C\equiv C}, \quad \mathrm{C=O}$

Option check

• A: Si $\rightarrow$ less effective than carbon
• B: Ge $\rightarrow$ less effective than carbon
• C: C $\rightarrow$ most effective
• D: Sn $\rightarrow$ least effective among these

Final answer

The element with greatest ability to form $p\pi$-$p\pi$ multiple bonds is: $\boxed{\mathrm{C}}$