Which of the following orders is correct?
(1) `SbH_(3)gt NH_(3) gt AsH_(3) gt PH_(3)-" Boiling Point"`
(2) `NH_(3) gt PH_(3) gt AsH_(3) gt SbH_(3)-" Thermal Stability"`
(3) `NH_(3) gt PH_(3) gt AsH_(3) gt SbH_(3) - "Basic Character"`
(4) `NH_(3) gt PH_(3) gt AsH_(3) gt SbH_(3)- "Bond Angle"`

Options

A. (1), (2) and (3) only
B. (2), (3) and (4) only
C. (1), (3) and (4) only
D. (1), (2), (3) and (4).

Answer

To determine the correct orders for the properties of the hydrides of group 15 elements (NH3, PH3, AsH3, SbH3), we will analyze each property one by one.

### 1. Boiling Point Order
**Analysis:**
- NH3 has a high boiling point due to hydrogen bonding, which is significant because nitrogen is highly electronegative.
- As we move down the group from NH3 to PH3, AsH3, and SbH3, the boiling points generally increase due to increased molecular weight and van der Waals forces.
- However, NH3 remains higher than PH3 due to hydrogen bonding.

**Conclusion:**
The correct order for boiling points is:
\[ \text{SbH}_3 > \text{NH}_3 > \text{AsH}_3 > \text{PH}_3 \]

### 2. Thermal Stability Order
**Analysis:**
- Thermal stability refers to the stability of the hydrides upon heating.
- The bond strength decreases as we go down the group due to the larger atomic size, which leads to weaker H-X bonds.
- NH3 has the strongest bond and is the most thermally stable, while SbH3 has the weakest bond and is the least stable.

**Conclusion:**
The correct order for thermal stability is:
\[ \text{NH}_3 > \text{PH}_3 > \text{AsH}_3 > \text{SbH}_3 \]

### 3. Basic Character Order
**Analysis:**
- Basic character increases down the group because the size of the atoms increases, making it easier to donate the lone pair of electrons.
- NH3 is the most basic because nitrogen has a high electronegativity and holds onto its electrons tightly, while SbH3 is the least basic.

**Conclusion:**
The correct order for basic character is:
\[ \text{NH}_3 > \text{PH}_3 > \text{AsH}_3 > \text{SbH}_3 \]

### 4. Bond Angle Order
**Analysis:**
- Bond angles are affected by hybridization and lone pair repulsion.
- NH3 has a bond angle of approximately 107.5° due to its sp³ hybridization and lone pair repulsion.
- PH3 has a bond angle of around 93.6° due to less effective hybridization and lone pair repulsion.
- As we move down the group, the bond angles decrease due to the decrease in hybridization effectiveness.

**Conclusion:**
The correct order for bond angles is:
\[ \text{NH}_3 > \text{PH}_3 > \text{AsH}_3 > \text{SbH}_3 \]

### Summary of Correct Orders:
1. **Boiling Point:** SbH3 > NH3 > AsH3 > PH3
2. **Thermal Stability:** NH3 > PH3 > AsH3 > SbH3
3. **Basic Character:** NH3 > PH3 > AsH3 > SbH3
4. **Bond Angle:** NH3 > PH3 > AsH3 > SbH3