The correct decreasing order of boiling points in the following is:

Q: The correct decreasing order of boiling points in the following is:

The correct decreasing order of boiling points in the following is:

Question

Accepted Answer

The correct decreasing order of boiling points for the given substances is $H_{2}O > HF > NH_{3}$, as stated in Option 2. Let's explore why this order is correct and why the other options are incorrect.

### Explanation for Option 2 ($H_{2}O > HF > NH_{3}$):

1. **Boiling Point of Water ($H_{2}O$):**
   - Water has the highest boiling point among the three substances due to its ability to form extensive hydrogen bonding networks. Each water molecule can form up to four hydrogen bonds (two as a donor and two as an acceptor), leading to a strong intermolecular force that requires more energy to break, resulting in a higher boiling point.

2. **Boiling Point of Hydrogen Fluoride ($HF$):**
   - HF also forms hydrogen bonds, but each HF molecule can form only two hydrogen bonds (one as a donor and one as an acceptor). Although HF has strong hydrogen bonds, the network is not as extensive as in water, leading to a lower boiling point compared to water.

3. **Boiling Point of Ammonia ($NH_{3}$):**
   - Ammonia can form hydrogen bonds as well, but it is less effective compared to water and HF. Each NH₃ molecule can form only one hydrogen bond as a donor and has three lone pairs that can accept hydrogen bonds. However, the overall hydrogen bonding network is weaker, resulting in the lowest boiling point among the three.

### Why Other Options are Incorrect:

1. **Option 1 ($HF > H_{2}O > NH_{3}$):**
   - This option incorrectly places HF above water. As explained, water has a more extensive hydrogen bonding network than HF, leading to a higher boiling point.

2. **Option 3 ($NH_{3} > HF > H_{2}O$):**
   - This option incorrectly places ammonia above both HF and water. Ammonia has the weakest hydrogen bonding among the three, resulting in the lowest boiling point.

3. **Option 4 ($NH_{3} > H_{2}O > HF$):**
   - This option incorrectly places ammonia above water and HF. As previously mentioned, ammonia has the weakest hydrogen bonding, leading to the lowest boiling point.

In conclusion, Option 2 is the correct order based on the strength and extent of hydrogen bonding in each substance, which directly influences their boiling points.