Which of the following shows dimerisation?

The element that has the least metallic character is ..........

Which one of the following statements is correct?

Which of the following is the correct decreasing order of Lewis acid strength of boron halides?

On the basis of reactions given below identify $X, Y, Z$.
$Boron \xleftarrow{Mg \, or \, Fe} X \xleftarrow{\Delta} B(OH)_3 + \text{Gas-}Z$
$B(OH)_3 \xleftarrow{H_2O} Y \xrightarrow{2NH_3/\Delta} \text{Inorganic benzene}$

In group $13$ of the long form of the periodic table,an element $X$ has a boiling point of $T_2 \ (K)$ and a melting point of $T_1 \ (K)$. Identify the element $X$ for which $T_2 - T_1 \ (K)$ is maximum.