The ionization energy of copper is higher than that of potassium though both have a \(4s^1\) configurationbecause the d-electrons in copper

form a poor shield, making copper smaller

The correct answer is option 1. form a poor shield, making copper smaller.

The d-electrons in copper form a poor shield, making copper smaller.

The ionization energy of an element is the energy required to remove an electron from an atom in its ground state. The ionization energy of an element is determined by the size of the atom and the shielding effect of the electrons.

In copper, the d-electrons are not as effective at shielding the 4s electrons from the nuclear charge as the s electrons in potassium. This is because the d-electrons are further away from the nucleus than the s electrons.

As a result, the 4s electrons in copper are more strongly attracted to the nucleus than the 4s electrons in potassium. This means that it takes more energy to remove an electron from copper than from potassium, and therefore the ionization energy of copper is higher than the ionization energy of potassium.

The other options are incorrect.

Option (2): The d-electrons in copper do not make copper bigger. In fact, they make copper smaller because they are not as effective at shielding the 4s electrons from the nuclear charge.

Option (3): The d-electrons in copper are not strongly shielded. In fact, they are weakly shielded, which is why they do not effectively shield the 4s electrons from the nuclear charge.

Option (4): The d-electrons in copper are not strongly shielded, which makes copper smaller.