Cyanogen gas is obtained in the reaction
A. \[{{CuS}}{{{O}}_{4\left( {{{aq}}} \right)}} + {{KCN}} \to \]
B. ${{{K}}_4}\left[ {{{Fe}}{{\left( {{{CN}}} \right)}_6}} \right]\xrightarrow{\Delta }$
C. ${{C}}{{{H}}_3}{{CN + }}{{{H}}_2}{{O}}\xrightarrow{\Delta }$
D. ${{C}}{{{H}}_3}{{CON}}{{{H}}_2} + {{{P}}_2}{{{O}}_5}\xrightarrow{\Delta }$

Hint: Before identifying the reaction, we have to find out what cyanogen is. From the name itself, it is obvious that it has a cyanide group. The chemical formula of cyanogen is ${\left( {{{CN}}} \right)_2}$. It can be prepared by different methods.

Complete step by step answer:
Cyanogen, ${\left( {{{CN}}} \right)_2}$is a type of gas. It is colorless and has a pungent odor. The bonding of this molecule is ${{N}} \equiv {{C - C}} \equiv {{N}}$. There is a single bond between two carbon atoms and a triple bond between carbon and nitrogen atoms. There are some isomers for cyanogen. But they are less stable than cyanogen. Some examples are iso cyanogen, diisocyanate and azodicarbon.
We know that cyanogen is prepared from cyanide compounds. One such example is given in the question. The balanced chemical equation can be represented as given below:
\[{{2CuS}}{{{O}}_{4\left( {{{aq}}} \right)}} + 4{{KCN}} \to {\left( {{{CN}}} \right)_2} + 2{{CuCN + 2}}{{{K}}_2}{{S}}{{{O}}_4}\]
When copper sulfate is reacted with potassium cyanide, copper cyanide and potassium sulfate are also formed along with cyanogen.
Thus cyanogen gas is obtained in the reaction \[{{CuS}}{{{O}}_{4\left( {{{aq}}} \right)}} + {{KCN}} \to \].

So, the correct answer is Option A.

Additional information:
Cyanogen can be prepared by oxidizing hydrogen cyanide with copper salt using chlorine with silicon dioxide or nitrogen dioxide as catalyst. An electrical spark or discharge is reacted with nitrogen and acetylene.
It is a very toxic gas since it reduces into cyanide and interrupts the mitochondrial electron transfer chain. Thus it causes headache, dizziness, convulsions, vomiting and even death. When cyanogen burns in oxygen, it produces a very hot natural flame.

Note: Cyanogen can be prepared by dehydration reaction of oxamide. The reaction is given below:
${{{H}}_2}{{NC}}\left( {{O}} \right){{C}}\left( {{O}} \right){{N}}{{{H}}_2} \to {{NCCN + 2}}{{{H}}_2}{{O}}$
It can also be prepared from cyanide compounds. Mercuric cyanide forms cyanogen and mercuric cyanide.