a) Dinitrogen pentoxide can be prepared by dehydrating nitric acid with  P₄O₁₀.
b) On heating  $Pb{\left(N{O}_3\right)}_2$  at ${400}^{o}C,$   a brown-coloured gas with diamagnetic nature is obtained.
c)  $68\%(w/w)HN{O}_3$  can be concentrated to 98% by using conc.  $H_{2}S{O}_4$.
d) The familiar brown ring test for nitrates depends on the ability of $F{e}^{+3}$   to reduce nitrates to nitric oxide. 
The correct statements are