Question:

$\textbf{Choose the correct statements about the hydrides of group 15 elements.}$
A. The stability of the hydrides decreases in the order \(\text{NH}_3 > \text{PH}_3 > \text{AsH}_3 > \text{SbH}_3 > \text{BiH}_3\)
B. The reducing ability of the hydrides increases in the order \(\text{NH}_3 < \text{PH}_3 < \text{AsH}_3 < \text{SbH}_3 < \text{BiH}_3\)
C. Among the hydrides, \(\text{NH}_3\) is a strong reducing agent while \(\text{BiH}_3\) is a mild reducing agent.
D. The basicity of the hydrides increases in the order \(\text{NH}_3 < \text{PH}_3 < \text{AsH}_3 < \text{SbH}_3 < \text{BiH}_3\)
Choose the most appropriate from the option given below:

Updated On: Feb 4, 2026
  • B and C only
  • C and D only
  • A and B only
  • A and D only
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The Correct Option is C

Solution and Explanation

Evaluate the given statements (A, B, C, D) regarding the properties of Group 15 hydrides to identify the correct ones.

Concept Used:

Key trends for Group 15 hydrides (ENH3):

  • Stability: Decreases down the group due to decrease in E–H bond dissociation enthalpy.
  • Reducing Character: Increases down the group as the E–H bond becomes weaker and easier to break.
  • Basicity: Decreases down the group due to decreased availability of the lone pair on the central atom (increase in size, decrease in electronegativity).

Step-by-Step Solution:

Step 1: Analyze Statement A: "The stability of the hydrides decreases in the order NH3 > PH3 > AsH3 > SbH3 > BiH3." This is correct. The E–H bond strength decreases down the group due to the increasing size of the central atom and poorer orbital overlap with hydrogen.

Step 2: Analyze Statement B: "The reducing ability of the hydrides increases in the order NH3 < PH3 < AsH3 < SbH3 < BiH3." This is correct. Reducing ability depends on the ease of E–H bond cleavage. As the bond becomes weaker down the group, the hydride can more readily donate H– (or H•), making it a stronger reducing agent.

Step 3: Analyze Statement C: "Among the hydrides, NH3 is a strong reducing agent while BiH3 is a mild reducing agent." This is incorrect. The trend is the opposite. NH3 is a very weak reducing agent (stable), while BiH3 is the strongest reducing agent in the group (very unstable and decomposes easily).

Step 4: Analyze Statement D: "The basicity of the hydrides increases in the order NH3 < PH3 < AsH3 < SbH3 < BiH3." This is incorrect. Basicity decreases down the group: NH3 > PH3 > AsH3 > SbH3 > BiH3. The lone pair on nitrogen in NH3 is most available for donation due to its small size and high electronegativity.

Thus, the correct statements are A and B only.

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