Chemistry - Complete Pblock- Question with Solution | TestHub

Carbon has a strong tendency to form $p\pi$-$p\pi$ multiple bonds with itself, such as in alkenes and alkynes. Thus, the first statement is correct.

${\text{BCl}}_3$ exists as a monomer because boron cannot expand its octet to form a dimer, whereas ${\text{AlCl}}_3$ exists as a dimer (${\text{Al}}_2{\text{Cl}}_6$) to complete its octet. Thus, the second statement is correct.

The catenation property depends on the element-element bond strength. The bond enthalpy decreases down the group, so the order of catenation is $C>>Si>Ge\approx Sn$. Thus, the third statement is correct.

Oxygen exhibits a $-2$ oxidation state in most of its compounds, but it also exhibits a $-1$ oxidation state in peroxides (e.g., ${\text{H}}_2{\text{O}}_2$), a $-1/2$ oxidation state in superoxides (e.g., ${\text{KO}}_2$), and positive oxidation states when bonded to fluorine (e.g., $+2$ in ${\text{OF}}_2$ and $+1$ in ${\text{O}}_2{\text{F}}_2$). Thus, the fourth statement is incorrect.

Answer: Oxygen exhibits only $-2$ oxidation state.