The correct order of increasing intermolecular hydrogen bond strength is

Options

A. `HCN lt H_2O lt NH_3`
B. `HCN lt CH_3 lt NH_3`
C. `CH_4 lt HCN lt NH_3`
D. `CH_4 lt NH_3 lt HCN`

Explanation

To determine the correct order of increasing intermolecular hydrogen bond strength, we need to analyze the hydrogen bonding capabilities of the given molecules. Here’s a step-by-step solution:

### Step 1: Understand Hydrogen Bonding
Hydrogen bonding occurs when a hydrogen atom covalently bonded to a highly electronegative atom (like N, O, or F) interacts with another electronegative atom. The strength of hydrogen bonds depends on the electronegativity of the atoms involved and the presence of lone pairs.

### Step 2: Identify the Molecules
The molecules we need to compare for hydrogen bonding strength are:
1. Ammonia (NH₃)
2. Water (H₂O)
3. Hydrogen cyanide (HCN)
4. Methane (CH₄)

### Step 3: Analyze Each Molecule
- **Water (H₂O)**: Water has two hydrogen atoms bonded to oxygen, which is highly electronegative and has two lone pairs. This allows for strong hydrogen bonding.

- **Ammonia (NH₃)**: Ammonia has one hydrogen atom bonded to nitrogen, which is also electronegative and has one lone pair. It can form hydrogen bonds, but they are generally weaker than those in water.

- **Hydrogen Cyanide (HCN)**: HCN has a hydrogen atom bonded to carbon, which is less electronegative than nitrogen and oxygen. However, the nitrogen in HCN can still participate in hydrogen bonding, but it is weaker than in NH₃ and H₂O.

- **Methane (CH₄)**: Methane does not have any electronegative atoms bonded to hydrogen, so it cannot form hydrogen bonds. Thus, it has the weakest intermolecular forces.

### Step 4: Order the Molecules by Hydrogen Bond Strength
Based on the analysis:
1. CH₄ (weakest, no hydrogen bonding)
2. HCN (weaker hydrogen bonding)
3. NH₃ (stronger hydrogen bonding)
4. H₂O (strongest hydrogen bonding)

### Final Order
The correct order of increasing intermolecular hydrogen bond strength is:
**CH₄ < HCN < NH₃ < H₂O**