Which of the following reactions will yield the crystalline variety of boron?

The correct statements among $I$ to $III$ regarding group $13$ element oxides are,
$I$. Boron trioxide is acidic
$II$. Oxides of aluminium and gallium are amphoteric
$III$. Oxides of indium and thallium are basic

Which of the following boron compounds is the hardest?

Which of the following statements is correct regarding boron hydrides?

The correct statements from the following are:
$(A)$ Ionic radii of trivalent cations of group $13$ elements decrease down the group.
$(B)$ Electronegativity of group $13$ elements decreases down the group.
$(C)$ Among the group $13$ elements, Boron has the highest first ionisation enthalpy.
$(D)$ The trichlorides and triiodides of group $13$ elements are covalent in nature.
Choose the correct answer from the options given below:

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