Question

Regarding the hydrides of group 15 elements \(EH_3\) \((E = N, P, As, Sb)\), select the correct statement(s):
[A.] The stability of hydrides decreases down the group.
[B.] The basicity of hydrides decreases down the group.
[C.] The reducing character increases down the group.
[D.] The boiling point increases down the group. Choose the correct answer:

• A. A, B, C & D
• B. A, B & C only
• C. B & C only
• D. A & D only

Hint:

Trends in group hydrides are governed by bond strength, atomic size, and intermolecular forces.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Group 15 elements form hydrides of the type \(EH_3\). Their properties change predictably down the group due to increasing atomic size and decreasing electronegativity of the central atom.
Step 2: Detailed Explanation:
A. Thermal Stability: As the size of 'E' increases down the group, the E-H bond length increases and bond dissociation enthalpy decreases. Thus, stability decreases (\(NH_3>PH_3>AsH_3>SbH_3>BiH_3\)). (True)
B. Basicity: Down the group, the size of the central atom increases, causing the lone pair of electrons to be distributed over a larger volume. The electron density decreases, making them less available for donation. Thus, basicity decreases. (True)
C. Reducing Character: Reducing character is linked to the ease of providing hydrogen. Since bond stability decreases down the group, the ease of releasing hydrogen increases. Thus, reducing character increases. (True)
D. Boiling Point: Boiling points generally increase down the group due to increasing Van der Waals forces. However, \(NH_3\) is an exception due to strong intermolecular hydrogen bonding, giving it a higher BP than \(PH_3\) and \(AsH_3\). The overall order is \(PH_3<AsH_3<NH_3<SbH_3<BiH_3\). Therefore, it does not strictly "increase down the group". (False)
Step 3: Final Answer:
Statements A, B, and C only are correct.