Dilute aqueous solution of $.......$ acid is used as an antibiotic.

Explain the following:
$(1)$ Aluminum forms $[AlF_6]^{3-}$ ion but boron does not form $[BF_6]^{3-}$ ion.
$(2)$ $PbX_2$ is more stable than $PbX_4$.

Which of the following statements are not correct?
$i$. Atomic radius of $Ga$ is less than that of $Al$
$ii$. The order of ionization enthalpy of group $13$ elements is $B > Al > Ga > In > Tl$
$iii$. Boron trioxide is amphoteric in nature

Which of the following reactions can be used to prepare diborane?
$I. BF_3 + LiAlH_4 \xrightarrow{\text{ether}}$
$II. BF_3 + NaH \xrightarrow{450 \ K}$
$III. Na_2B_4O_7 + H_2O \longrightarrow$
$IV. NaBH_4 + I_2 \longrightarrow$

Which of the following is the weakest acid?

Why does boron trifluoride $(BF_3)$ behave as a Lewis acid?