Concentrated nitric acid,upon long standing,turns yellow-brown due to the formation of

Among the following,cyclic species are :
$I$. $H_5P_3O_{10}$ $II$. $[B_3O_3(OH)_5]^{2-}$ $III$. $H_5P_5O_{15}$ $IV$. $P_3N_3Cl_6$

The number of $P-O-P$ bonds in cyclic metaphosphoric acid is

Which of the following is $NOT$ a property of red phosphorus?

Which one of the following properties is $not$ shown by $NO$?

Which one of the following is not correct?