What is the structure of soluble complex formed, when $CuS{{O}_{4}}$ is treated with ethylamine?
A. ${{[Cu{{(C{{H}_{3}}C{{H}_{2}}N{{H}_{2}})}_{4}}]}^{2+}}SO_{4}^{2-}$
B. ${{[Cu{{(C{{H}_{3}}C{{H}_{2}}N{{H}_{2}})}_{2}}]}^{2+}}SO_{4}^{2-}$
C. ${{[C{{u}_{2}}{{(C{{H}_{3}}C{{H}_{2}}N{{H}_{2}})}_{4}}]}^{2+}}SO_{4}^{2-}$
D. ${{[C{{u}_{2}}{{(C{{H}_{3}}C{{H}_{2}}N{{H}_{2}})}_{2}}]}^{2+}}SO_{4}^{2-}$

Hint: Ethylamine is a monodentate ligand means it can donate a lone pair of electrons to the metals and forms a complex called coordination complex. At the time of forming complexes single ligands won't participate in reaction with metal. The number of ligands involved in the formation of the complex is going to depend on the metal.

Complete step by step solution:
- In the question it is asked to find the structure of the soluble complex formed when copper sulphate is going to react with ethylamine.
- The structure of ethylamine is ${{C}_{2}}{{H}_{5}}N{{H}_{2}}$ .
- The chemical reaction of ethyl amine with copper sulphate is as follows.
\[CuS{{O}_{4}}+4C{{H}_{3}}C{{H}_{2}}N{{H}_{2}}\to {{[Cu{{(C{{H}_{3}}C{{H}_{2}}N{{H}_{2}})}_{4}}]}^{2+}}SO_{4}^{2-}\]
- From the above chemical reaction we can say that one mole of copper sulphate is going to react with four moles of ethylamine and forms one mole of the copper coordination complex and one moles of the sulphate anion.
- The formed coordination complex ${{[Cu{{(C{{H}_{3}}C{{H}_{2}}N{{H}_{2}})}_{4}}]}^{2+}}SO_{4}^{2-}$ is also soluble in water due to ionic nature.
- Always copper forms colored complexes with the ligands.

Therefore the correct option is A.

Note: The ligand which donates a single lone pair of electrons then the ligand is called monodentate ligand. If a ligand donates four lone pairs of electrons to the metal atom then the ligand is called tetradentate ligand. The ligand which donates six lone pairs of electrons then the ligand is called hexadentate ligand. Denticity means the capability to donate the lone pair of electrons.