**(i) H**_{2}^{+1}SO_{3}^{-2}

^{}

However, the O.N. of S cannot be +8. S has six valence electrons. Therefore, the O.N. of S cannot be more than +6.

The structure of H_{2}SO_{5} is shown as follows:

Therefore, the O.N. of S is +6.

**(ii)** Cr_{2}O_{7}^{2-}

Here, there is no fallacy about the O.N. of Cr in Cr_{2}O_{7}^{2-}

The structure of Cr_{2}O_{7}^{2-}

is shown as follows:

Here, each of the two Cr atoms exhibits the O.N. of +6.

**(iii) NO**_{3}^{-}

^{}

Here, there is no fallacy about the O.N. of N in NO_{3}^{-}

The structure of NO_{3}^{-}

^{}

is shown as follows: The N atom exhibits the O.N. of +5.