In which of the following substances will hydrogen bond be strongest?

Options

A. HCl
B. `H_(2)O`
C. HI
D. `H_(2)S`

Explanation

To determine in which of the given substances the hydrogen bond will be strongest, we need to analyze the four substances: HCl, H2O, HI, and H2S. The strength of hydrogen bonds is influenced by two main factors:

1. **Electronegativity of the atom to which hydrogen is bonded**: The more electronegative the atom, the stronger the hydrogen bond.
2. **Size of the atom to which hydrogen is bonded**: Smaller atoms can form stronger hydrogen bonds due to closer proximity to the hydrogen atom.

Let's analyze each substance:

### Step 1: Identify the electronegativity of the atoms
- **HCl**: Chlorine (Cl) has an electronegativity of about 3.16.
- **H2O**: Oxygen (O) has an electronegativity of about 3.44.
- **HI**: Iodine (I) has an electronegativity of about 2.66.
- **H2S**: Sulfur (S) has an electronegativity of about 2.58.

### Step 2: Compare the electronegativities
From the values above, we can see that:
- Oxygen (in H2O) is the most electronegative atom among the four.
- Chlorine (in HCl) is next, followed by iodine (in HI) and sulfur (in H2S).

### Step 3: Consider the size of the atoms
- **Oxygen** is the smallest atom among Cl, O, I, and S.
- **Chlorine** is larger than oxygen but smaller than iodine and sulfur.
- **Iodine** is larger than chlorine and sulfur.
- **Sulfur** is larger than both chlorine and oxygen.

### Step 4: Analyze the hydrogen bonds
- In **H2O**, the hydrogen is bonded to the most electronegative atom (O) and the size of oxygen is small, allowing for a strong hydrogen bond.
- In **HCl**, the hydrogen is bonded to chlorine, which is less electronegative than oxygen.
- In **HI**, the hydrogen is bonded to iodine, which is even less electronegative and larger than chlorine.
- In **H2S**, the hydrogen is bonded to sulfur, which is the least electronegative and larger than both chlorine and oxygen.

### Conclusion
Since H2O has the most electronegative atom (O) and a small size, it will have the strongest hydrogen bonds compared to HCl, HI, and H2S.

**Final Answer**: The strongest hydrogen bond will be found in **H2O** (water).

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