Which of the following allotropes of phosphorus is the most stable,has a graphite-like structure,and is a conductor of electricity?

Which one of the following is correct with respect to basic character?

All alums contain ......

Which of the following statements is $NOT$ correct?

On adding water to $BiCl_3$ solution in $HCl$,the compound produced is

Account for the following observations:
$(A)$ $AlCl_3$ is a Lewis acid.
$(B)$ Though fluorine is more electronegative than chlorine yet $BF_3$ is a weaker Lewis acid than $BCl_3$.
$(C)$ $PbO_2$ is a stronger oxidizing agent than $SnO_2$.
$(D)$ The $+1$ oxidation state of thallium is more stable than its $+3$ state.