The atomic number of Cu is 29. The EAN ( Effective Atomic Number) of Cu in ${{\left[ Cu{{\left( N{{H}_{3}} \right)}_{4}} \right]}^{2+}}$

Hint: Effective Atomic Number is defined as the number which is the total no. of electrons present around the central metal atom in a complex. It contains the bonding electrons of the metal and the neighbouring atoms which can be donating as well as receiving. There is a formula to calculate Effective Atomic Number.
EAN = Atomic number(Z) - Oxidation number + 2 × Coordination number


Complete Solution :
In this question we have already given the stoic number of Cu which is 29, the oxidation number here is +2 and coordination number here is 4.
- Always remember that there are certain different rules when the oxidation number of a coordination complex is to be found out. The overall charge of the complex is subtracted from the individual charges of the neighbouring atoms. ${{\left[ Cu{{\left( N{{H}_{3}} \right)}_{4}} \right]}^{2+}}$, in this complex , the overall charge of the complex is +2.
$OxidationNo. = 2-\left( charge~on~N{{H}_{3}} \right)\times 4$
Since there is no formal charge present on the Ammonia molecule,
Oxidation No.= 2 - (0) × 4
Oxidation No. = +2.
Now, we can find the Effective Atomic Number:
EAN = 29 - 2 + (2 × 4)
EAN = 29 - 2 + 8
EAN = 35
Therefore, the Effective Atomic Number of Cu is 35.

Note: The Coordination number of a complex compound is the number of molecules present around the central metal atom. In this question, the ${{\left[ Cu{{\left( N{{H}_{3}} \right)}_{4}} \right]}^{2+}}$ Copper have 4 Ammonia molecules present around it. Therefore, the coordination number is 4 in this question.