Answer the question on the basis of passage given below:

Second period elements of p-Block differ from the rest of their group members due to their small atomic size, high electronegativity, high ionization enthalpy and absence of d-orbitals.

The elements from the second period like C, N, O have unique property of forming pa pa multiple bonds whereas other heavier elements of p-block form da pa multiple bonds. This changes the properties of second period elements to great extent. Also the single bond strength of the p-block elements with their own atoms gets affected by their atomic size and presence of lone pairs.

Inert pair effect also affects the properties of the p-Block elements especially for those elements which are present from 4th period onward and this happens due to poor screening effect of inner (n-1) d subshell electrons.

Phosphorus forms \(PF_5\) but nitrogen cannot form \(NF_5\) as:

Nitrogen cannot extend its octet due to absence of d-orbitals in it

The correct answer is option 4. Nitrogen cannot extend its octet due to absence of d-orbitals in it.

Nitrogen, like many elements, typically follows the octet rule, which states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with eight electrons in their valence shell. However, nitrogen lacks d-orbitals in its valence shell. In the ground state, nitrogen has three p-orbitals available for bonding, allowing it to form a maximum of three covalent bonds and thus accommodate a maximum of six electrons in its valence shell. This means that nitrogen typically forms molecules where it has eight electrons, following the octet rule. However, nitrogen does not have the ability to accommodate additional electrons beyond its octet because there are no d-orbitals available to participate in bonding.

Phosphorus, unlike nitrogen, has vacant d-orbitals available in its valence shell. This allows phosphorus to accommodate additional electrons beyond its octet when forming compounds. In the case of \(PF_5\), phosphorus forms five covalent bonds with fluorine atoms, utilizing its d-orbitals to accommodate the extra electrons from the fluorine atoms. Phosphorus can thus exceed the octet rule and form compounds with more than eight electrons around it.

While differences in electronegativity and atomic size between nitrogen and phosphorus do influence their chemical behavior, they are not the primary reasons why nitrogen cannot form \(NF_5\). Nitrogen's inability to form compounds like \(NF_5\) primarily stems from its inability to extend its octet beyond eight electrons, which is due to the absence of d-orbitals in its valence shell.

Therefore, the absence of d-orbitals in nitrogen's valence shell is the key reason why nitrogen cannot form compounds like \(NF_5\), while phosphorus, with its available d-orbitals, can form compounds like \(PF_5\) by exceeding the octet rule.