The correct sequence of decrease in the basic strength of the following hydrides is:

Options

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

Explanation

To determine the correct sequence of decreasing basic strength of the hydrides of the nitrogen family (Group 15), we need to analyze the basic strength of each hydride based on their ability to donate a lone pair of electrons. The hydrides we are considering are NH₃ (ammonia), PH₃ (phosphine), AsH₃ (arsine), SbH₃ (stibine), and BiH₃ (bismuthine).

### Step-by-Step Solution:

1. **Understanding Basic Strength**: Basic strength refers to the ability of a compound to donate a lone pair of electrons. The more readily a compound can donate its lone pair, the stronger the base it is.

2. **Analyzing the Hydrides**: The hydrides of the nitrogen family we are considering are:
- NH₃ (Ammonia)
- PH₃ (Phosphine)
- AsH₃ (Arsine)
- SbH₃ (Stibine)
- BiH₃ (Bismuthine)

3. **Trends in Basic Strength**:
- Basic strength generally decreases down the group due to the increase in atomic size and the corresponding decrease in electron density.
- As we move down the group from nitrogen to bismuth, the size of the atoms increases, which leads to a decrease in the ability of the lone pair to be donated.

4. **Comparing Basic Strength**:
- **NH₃**: Has the smallest size and highest electron density, making it the strongest base.
- **PH₃**: Larger than NH₃, but still retains some basic character.
- **AsH₃**: Even larger, with decreased electron density compared to PH₃.
- **SbH₃**: Further decrease in basicity due to increased size.
- **BiH₃**: The largest and least basic due to the lowest electron density.

5. **Final Order of Basic Strength**: Based on the above analysis, the order of decreasing basic strength of the hydrides is:
- NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃

### Conclusion:
The correct sequence of decreasing basic strength of the hydrides is:
**NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃**