Answer the question on basis of passage given below:

P block elements are placed in groups 13 to 18 of the periodic table. Their valence shell electronic configuration is \(ns^2\, \ np^{1-6}\). Group 16 of of the p-block elements are known as the group of chalcogens having \(ns^2\, \ np^4\) as their general electronic configuration. They exhibit number of oxidation states but the stability of \(-2\) oxidation state decreases down the group. They are sometimes also known as group of chalcogens as the name is derived from the Greek word for brass and points to the association of sulphur and its congeners with copper. Their ionization enthalpy decreases down the group. Oxygen shows anomalous behaviour due to its small size and high electronegativity.

Given below are the hydrides  formed by group 15 elements. Choose the correct decreasing order of basicity of the following hydrides

A. \(AsH_3\)

B. \(PH_3\)

C. \(NH_3\)

D. \(BiH_3\)

E. \(SbH_3\)

Choose the correct answer from the options given below:

C, B, A, E, D

The correct answer is option 1. C, B, A, E, D.

Let us delve into the basicity of the hydrides of Group 15 elements in detail. The Group 15 hydrides are \(NH_3\) (ammonia), \(PH_3\) (phosphine), \(AsH_3\) (arsine), \(SbH_3\) (stibine), and \(BiH_3\) (bismuth hydride). Basicity here refers to the ability of these hydrides to donate a lone pair of electrons to a proton (H⁺).

Basicity of a hydride depends on the availability of the lone pair of electrons on the central atom (N, P, As, Sb, Bi) to bond with a proton. Key factors influencing basicity include:

Electronegativity: More electronegative atoms hold their lone pairs more tightly, making them less available for bonding with protons. Therefore, higher electronegativity generally means lower basicity.

Size of the Atom: Larger atoms have lone pairs that are more diffuse, making them more available for bonding with protons, but less tightly bound compared to smaller atoms.

Electron Density: Greater electron density on the central atom usually increases basicity, as the lone pair is more readily available to bond with a proton.

Analysis of Each Hydride

C. Ammonia (\(NH_3\))

Central Atom: Nitrogen

Electronegativity: High (3.0 on the Pauling scale)

Size: Small

Lone Pair Availability: Nitrogen’s lone pair is highly available due to its small size and high electronegativity. Hence, ammonia is a strong base.

B. Phosphine (\(PH_3\))

Central Atom: Phosphorus

Electronegativity: Moderate (2.19 on the Pauling scale)

Size: Larger than nitrogen

Lone Pair Availability: Phosphorus has a lone pair that is less tightly held compared to nitrogen, making it less basic than ammonia but still fairly available.

A. Arsine (\(AsH_3\))

Central Atom: Arsenic

Electronegativity: Lower (2.18 on the Pauling scale)

Size: Larger than phosphorus

Lone Pair Availability: The lone pair on arsenic is even less tightly held and more diffuse compared to phosphorus. However, arsenic’s lower electronegativity makes it less basic than phosphine.

E. Stibine (\(SbH_3\))

Central Atom: Antimony

Electronegativity: Lower (1.89 on the Pauling scale)

Size: Larger than arsenic

Lone Pair Availability: The lone pair on antimony is very diffuse and less tightly bound. The basicity is quite low compared to arsine due to the large size and low electronegativity of antimony.

D. Bismuth Hydride (\(BiH_3\))

Central Atom: Bismuth

Electronegativity: Lowest among Group 15 elements (1.93 on the Pauling scale)

Size: Largest among these elements

Lone Pair Availability: Bismuth has a very diffuse lone pair that is poorly available for bonding with protons. Thus, bismuth hydride is the least basic among these hydrides.

Therefore, the correct decreasing order of basicity is: \(NH_3 > PH_3 > AsH_3 > SbH_3 > BiH_3\)

Thus, the correct option is: 1. C, B, A, E, D