In which among the following pairs are both the elements metalloids?

Choose the typical element.

The set of amphoteric oxides among $ZnO$,$Tl_2O_3$,$In_2O_3$,$B_2O_3$,$PbO$,$SnO_2$ is

The size of $Be^{2+}$ and $Al^{3+}$ is not so close,but they show a diagonal relationship due to:

With the help of the following reactions,arrange the metals $A$,$B$,$D$,and $E$ in decreasing order of their reactivity:
$(I)$ $B + ANO_3 \longrightarrow BNO_3 + A$
$(II)$ $A + HCl \longrightarrow ACl + \frac{1}{2} H_2$
$(III)$ $D + ECl \longrightarrow DCl + E$
$(IV)$ $D + HNO_3 \longrightarrow$ $H_2$ gas is not evolved

Explain the periodic properties of elements and their reactivity trends in the periodic table.