Which statement of the following is false for isoelectronic species?

Their outer electronic configuration is different.

The correct answer is option 3. Their outer electronic configuration is different.

Let us go through each statement again to clearly explain why it is true or false for isoelectronic species:

1. They have the same outer electronic configuration.

Isoelectronic species have the same total number of electrons, meaning they have the same electron configuration overall. This includes the outer (valence) electron configuration. For example, both \( \text{N}_2 \) and \( \text{CO} \) are isoelectronic, each having 10 electrons. Therefore, this statement is true.

2. Their bond orders are the same.

Bond order depends on the specific types of atoms involved and how electrons are distributed in bonding and anti-bonding orbitals. Even if species are isoelectronic, the bond order can differ. For example, \( \text{N}_2 \) has a bond order of 3, while \( \text{CO} \) has a bond order of 3 as well, but this isn't always the case for all isoelectronic species. Thus, this statement is not universally true and can be false depending on the context.

3. Their outer electronic configuration is different.

Isoelectronic species, by definition, have the same total number of electrons and the same electronic configuration, including the outer (valence) shell. Therefore, this statement is false because it contradicts the very definition of isoelectronic species.

4. Their bond energies are nearly the same.

Bond energy depends on the specific nature of the bonds formed between the atoms and can vary even among isoelectronic species. For example, while \( \text{N}_2 \) and \( \text{CO} \) might have similar bond energies due to their similar bonding situation, this is not a general rule. Hence, this statement is not universally true and can be considered false in a general context.

Based on these explanations, the clear false statement is: (3) Their outer electronic configuration is different.

This is false because isoelectronic species must have the same outer electronic configuration as part of their definition.