The incorrect statement regarding `15 th` group hydrides `(EH_(3))[E=N,P,As,Sb,Bi]`

Options

A. `NH_(3)gtPH_(3)gtAsH_(3)gtSbH_(3)gtBiH_(3)` (Thermal Stability)
B. `N-HgtP-HgtAs-H-Sb-HgtBi-H` (E-H bond Dissociation Enthalpy)
C. `NH_(3)gtPH_(3)gtAsH_(3)gtSbH_(3)gtBiH_(3)` (Reducing Character)
D. `NH_(3)gtPH_(3)gtAsH_(3)gtSbH_(3)gtBiH_(3)` (Basicity)

Answer

To solve the question regarding the incorrect statement about the 15th group hydrides (EH3) where E = N, P, As, Sb, Bi, we will analyze each statement related to these hydrides step by step.

### Step 1: Analyze Thermal Stability
- **Statement**: The thermal stability of the hydrides decreases as we move down the group from NH3 to BiH3.
- **Explanation**: This is true because as we move down the group, the size of the central atom increases, leading to longer bond lengths and weaker bonds. Thus, NH3 is more thermally stable than PH3, which is more stable than AsH3, and so on.

### Step 2: Analyze Bond Dissociation Enthalpy
- **Statement**: The bond dissociation enthalpy decreases down the group from NH3 to BiH3.
- **Explanation**: This is also true. As the bond length increases due to the larger size of the central atom, the bond strength decreases, which means less energy is required to break the bonds. Therefore, NH3 has the highest bond dissociation enthalpy, followed by PH3, AsH3, SbH3, and BiH3.

### Step 3: Analyze Reducing Character
- **Statement**: The reducing character increases down the group from NH3 to BiH3.
- **Explanation**: This statement is true. As we move down the group, the bond strength decreases, and the electronegativity of the central atom also decreases, making the hydrides better reducing agents. Therefore, the reducing character increases from NH3 to BiH3.

### Step 4: Analyze Basicity
- **Statement**: The basicity of the hydrides decreases down the group from NH3 to BiH3.
- **Explanation**: This is true as well. NH3 is a strong base due to its small size and high electron density, which allows it to donate electron pairs effectively. As we move down the group, the size increases, and the electron density becomes more diffuse, leading to decreased basicity.

### Conclusion
After analyzing all the statements, we find that all the statements regarding thermal stability, bond dissociation enthalpy, reducing character, and basicity are correct. Therefore, the incorrect statement is about the reducing character, which states that it decreases down the group, which is false.

### Final Answer
The incorrect statement regarding the 15th group hydrides (EH3) is that the reducing character decreases down the group.

---