Formal charge on sulphur atom in the following three Lewis structures I, II and III respectively is
\[
\text{I.}\quad \ddot{S}=C=\ddot{N}
\]
\[
\text{II.}\quad :S-C\equiv N:
\]
\[
\text{III.}\quad :S\equiv C-N:
\]
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Use
\[
\text{Formal Charge}
=
\text{Valence Electrons}
-
\text{Lone Pair Electrons}
-
\frac{\text{Bonding Electrons}}{2}.
\]
For sulphur:
\[
V=6.
\]
More bonds generally make the formal charge more positive, while more lone pairs make it more negative.