Question

The basic character of the hydrides of 15 group elements decreases in the order:

• A. NH₃>PH₃>AsH₃>SbH₃
• B. SbH₃>AsH₃>PH₃>NH
• C. NH₃>AsH₃>PH₃>SbH₃
• D. NH₃>SbH₃>PH₃>AsH₃
• E. SbH₃>PH₃>AsH₃>NH₃

Answer 1

The Correct Option is A

Group 15 hydrides basicity trend:

• Basicity decreases down the group
• NH₃ > PH₃ > AsH₃ > SbH₃
• Reason: Decreasing electronegativity difference with H down the group
• Lone pair availability decreases with increasing atomic size

Thus, the correct option is (A): NH₃ > PH₃ > AsH₃ > SbH₃.

Answer 2

1. Understanding the basic character of hydrides:

The basic character of a compound depends on its ability to donate a lone pair of electrons. For the hydrides of group 15 elements (NH₃, PH₃, AsH₃, SbH₃), the basicity decreases as the size of the central atom increases. This is because:

• As the size of the central atom increases, the lone pair of electrons is held less tightly due to the larger atomic radius.
• The electron density on the central atom decreases, making it less available for donation.
• Hence, the ability to donate the lone pair (basicity) decreases down the group.

2. Analyze the hydrides of group 15 elements:

• NH₃: Nitrogen is the smallest and most electronegative element in group 15. The lone pair on nitrogen is held tightly and is readily available for donation, making NH₃ the strongest base among the group 15 hydrides.
• PH₃: Phosphorus is larger than nitrogen, so the lone pair is less tightly held. PH₃ is less basic than NH₃.
• AsH₃: Arsenic is larger than phosphorus, further reducing the availability of the lone pair. AsH₃ is less basic than PH₃.
• SbH₃: Antimony is the largest of the four elements, and the lone pair is least available for donation. SbH₃ is the weakest base among the group 15 hydrides.

3. Arrange the hydrides in order of decreasing basicity:

• The basic character decreases in the order: NH₃ > PH₃ > AsH₃ > SbH₃.

4. Final answer:

The correct option is (A) NH₃ > PH₃ > AsH₃ > SbH₃.