Fifth group elements form hydrides to type `AH_(3)`. The hydrides have a lone pair of electrons. The hydries are reducing in nature and the reducing power is related to the stability of A-H bonds. The hydrides are covalent and low boiling. Their boiling points depends on their ability to from hydrogen bond and their molecular size which decide the intermolcular forces in the hydrides .
Reducing power of V-group hydrides are in order :

Options

A. `NH_(3) gt PH_(3) gt AsH_(3) gt SbH_(3) gt BiH_(3)`
B. `BiH_(3) gt SbH_(3) gt AsH_(3) gt PH_(3) gt NH_(3)`
C. `PH_(3) gt NH_(3) gt AsH_(3) gt SbH_(3) gt BiH_(3)`
D. `BiH_(3) gt SbH_(3) gt AsH_(3) gt NH_(3) gt PH_(3)`

Explanation

To determine the reducing power of the fifth group hydrides (Group 15 elements) of the type \( AH_3 \), we can analyze the properties of these hydrides and how they change down the group. Let's break down the solution step by step.

### Step 1: Identify the Group 15 Hydrides
The Group 15 elements that form hydrides include:
- Nitrogen (N) → Ammonia (\( NH_3 \))
- Phosphorus (P) → Phosphine (\( PH_3 \))
- Arsenic (As) → Arsenic Hydride (\( AsH_3 \))
- Antimony (Sb) → Antimony Hydride (\( SbH_3 \))
- Bismuth (Bi) → Bismuth Hydride (\( BiH_3 \))

### Step 2: Understand the Reducing Power
The reducing power of these hydrides is related to their ability to donate electrons (or liberate hydrogen). The stability of the \( A-H \) bond plays a crucial role in determining how easily the hydride can release hydrogen.

### Step 3: Analyze the Stability of the \( A-H \) Bonds
As we move down the group from nitrogen to bismuth:
- The size of the central atom increases.
- The bond strength of \( A-H \) bonds decreases due to the larger atomic size and the corresponding increase in bond length.

### Step 4: Relate Stability to Reducing Power
- As the thermal stability of the hydrides decreases (weaker \( A-H \) bonds), the tendency of the hydrides to liberate hydrogen increases.
- Therefore, the reducing power increases down the group.

### Step 5: Order of Reducing Power
Based on the above analysis, the order of reducing power of the Group 15 hydrides is:
- \( NH_3 \) (least reducing power, most stable)
- \( PH_3 \)
- \( AsH_3 \)
- \( SbH_3 \)
- \( BiH_3 \) (most reducing power, least stable)

Thus, the reducing power of the fifth group hydrides in order is:
\[ BiH_3 > SbH_3 > AsH_3 > PH_3 > NH_3 \]

### Final Answer
The reducing power of the fifth group hydrides is in the order:
\[ BiH_3 > SbH_3 > AsH_3 > PH_3 > NH_3 \]

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