Question

Identify the incorrect statement from the following:

• A. \(ECl_3\), \((E=B \text{ and } Al)\), is a monomer when \(E=B\) and a dimer when \(E=Al\).
• B. The order of catenation property of Group 14 elements is \(C >> Si>Ge = Sn\).
• C. Oxygen exhibits only \(-2\) oxidation state.
• D. Carbon has the ability to form \(p\pi-p\pi\) multiple bond with itself.

Hint:

Oxygen commonly shows \(-2\), but it can also show \(-1\), \(-\frac{1}{2}\), \(+1\), and \(+2\) oxidation states in special compounds.

Answer 1

The Correct Option is C

Step 1: Check statement (A).
Boron trichloride is: \[ BCl_3 \] It exists as a monomer because boron is small and back bonding can stabilize the molecule. Aluminium chloride: \[ AlCl_3 \] can exist as a dimer: \[ Al_2Cl_6 \] due to electron deficiency and bridging chlorine atoms. So statement (A) is correct.

Step 2: Check statement (B).
Catenation means the ability of an element to form bonds with itself. Carbon has the maximum catenation tendency because:
• C--C bond is strong.
• Carbon has small atomic size.
• Carbon forms stable chains and rings. In Group 14, catenation decreases down the group. So: \[ C >> Si > Ge = Sn \] is acceptable. Thus, statement (B) is correct.

Step 3: Check statement (C).
Oxygen commonly shows oxidation state: \[ -2. \] But it does not show only \(-2\) oxidation state. For example: \[ \ce{H2O2} \] has oxygen in oxidation state: \[ -1. \] In superoxides, oxygen shows: \[ -\frac{1}{2}. \] In \(\ce{OF2}\), oxygen shows: \[ +2. \] Therefore, statement (C) is incorrect.

Step 4: Check statement (D).
Carbon can form \(p\pi-p\pi\) multiple bonds with itself. Examples are: \[ \ce{C=C} \] and: \[ \ce{C#C}. \] So statement (D) is correct. Hence, the incorrect statement is: \[ \text{Oxygen exhibits only }-2\text{ oxidation state.} \]