Identifying the Incorrect Chemistry Statement

The question asks to identify the statement about chemical properties that is incorrect.

Analysis of Statements

• Statement 1: This statement discusses the structure of $ECl_3$ where E is Boron (B) or Aluminum (Al).
  • Boron trichloride ($BCl_3$) is electron deficient and exists as a monomer.
  • Aluminum trichloride ($AlCl_3$) typically exists as a dimer ($Al_2Cl_6$) in the solid and gaseous states at lower temperatures, becoming monomeric at higher temperatures.
  Therefore, the description of $BCl_3$ as a monomer and $AlCl_3$ as a dimer is generally considered correct under standard conditions.
• Statement 2: This concerns the catenation property of Group 14 elements. Catenation is the ability of atoms to link together covalently to form chain or ring structures.
  • Carbon (C) exhibits the strongest catenation due to its strong C-C single and multiple bonds.
  • Silicon (Si) also shows catenation, forming polysilanes, but the Si-Si bonds are weaker than C-C bonds.
  • Germanium (Ge) and Tin (Sn) exhibit limited catenation due to progressively weaker M-M bonds.
  The order $C \gg Si > Ge \approx Sn$ accurately reflects this trend. This statement is correct.
• Statement 3: This statement claims Oxygen exhibits *only* a -2 oxidation state.
  • Oxygen typically has an oxidation state of -2 in most compounds (e.g., $H_2O$, $CO_2$).
  • However, Oxygen exhibits other oxidation states:
    • -1 in peroxides (e.g., $H_2O_2$).
    • -1/2 in superoxides (e.g., $KO_2$).
    • 0 in elemental form ($O_2$).
    • Positive oxidation states, like +1 (in $OF_2$, where F is considered) and +2 (in $OF_2$, where F is more electronegative). Note: $OF_2$ has O as +2, $O_2F_2$ has O as +1.
  Since Oxygen can exhibit oxidation states other than -2, the claim that it exhibits *only* -2 is incorrect.
• Statement 4: This statement addresses the ability of Carbon to form $p\pi-p\pi$ multiple bonds with itself.
  • Carbon atoms readily form double bonds ($C=C$) and triple bonds ($C\equiv C$) with each other.
  • These multiple bonds involve the sideways overlap of parallel p-orbitals, known as $p\pi-p\pi$ bonding.
  This capability is fundamental to organic chemistry and is a correct statement.

Conclusion

Based on the analysis, the statement that Oxygen exhibits only a -2 oxidation state is factually incorrect because Oxygen displays various oxidation states depending on the compound.