Which of the following compounds is the most explosive?

Which of the following is not correct?

Which of the following elements forms $p\pi-p\pi$ bond with itself?

Which of the following oxides of nitrogen is coloured?

The number of ions from the following that are expected to behave as oxidising agents is:
$Sn^{4+}$,$Sn^{2+}$,$Pb^{2+}$,$Tl^{3+}$,$Pb^{4+}$,$Tl^{+}$

$PCl_5$ exists but $NCl_5$ does not because