Structure And Properties Of Atoms

Step 1: Understanding electron configuration.
To determine the number of unpaired electrons, we need to look at the electron configurations of the ions:

- Cu has the electron configuration [Ar] 3d , which has one unpaired electron.

- Na has the electron configuration [Ne], which has no unpaired electrons.

- Cr has the electron configuration [Ar] 3d , which has three unpaired electrons.

- Fe has the electron configuration [Ar] 3d , which has five unpaired electrons.

Step 2: Conclusion.
The correct answer is (D) Fe , which has the maximum number of unpaired electrons.

To determine the energy required to move the electron from its ground state to the first excited state in a hydrogen atom, we first need to understand the energy levels of a hydrogen atom. The energy of an electron in the n^th energy level is given by the formula:
E_n = -13.6 / n² eV.
In the ground state (n = 1), the energy is:
E₁ = -13.6 / 1² = -13.6 eV.
In the first excited state (n = 2), the energy is:
E₂ = -13.6 / 2² = -13.6 / 4 = -3.4 eV.
To find the energy required to move the electron from the ground state to the first excited state, we calculate the difference between these two energy levels:
ΔE = E₂ - E₁ = -3.4 eV - (-13.6 eV) = 10.2 eV.
Thus, the energy required is 10.20 eV.