Which one is a Lewis acid?

Which of the following molecules acts as a Lewis acid?

Which of the following bonds has the highest bond energy?

The $X-X$ bond length is $1.00 \mathring{A}$ and $C-C$ bond length is $1.54 \mathring{A}$. If $EN$ of $X$ and $C$ are $3.0$ and $2.0$ respectively,the $C-X$ bond length is likely to be ............ $\mathring{A}$.

Which of the following molecules does $NOT$ obey the octet rule?

The number of electrons involved in the bond formation of $N_2$ molecule is: