Which one of the following is strongest acid ?

Options

A. `H_2 S`
B. `H_2 Se`
C. `H_2 O`
D. `H_2 Te`

Explanation

To determine which of the given compounds is the strongest acid, we will analyze the hydrides of the oxygen family: H2S, H2Se, H2O, and H2Te.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds in question are H2S (hydrogen sulfide), H2Se (hydrogen selenide), H2O (water), and H2Te (hydrogen telluride).

2. **Understand Acidity**: Acidity is defined by the ability of a compound to donate protons (H+ ions). The stronger the acid, the more readily it donates protons.

3. **Consider the Group Trend**: These compounds belong to the group 16 elements (the oxygen family). As we move down the group from oxygen (O) to tellurium (Te), the size of the elements increases.

4. **Analyze Bond Strength**: The strength of the E-H bond (where E is the group 16 element) decreases as we move down the group. This is because the larger the element, the less effective the overlap with hydrogen, leading to a weaker bond.

5. **Relate Bond Strength to Acidity**: A weaker E-H bond means that it is easier for the compound to release a proton (H+). Therefore, as we move down the group, the acidity increases.

6. **Rank the Acids**: Based on the trend, we can rank the acids in terms of their strength:
- H2O (strongest bond, weakest acid)
- H2S
- H2Se
- H2Te (weakest bond, strongest acid)

7. **Conclusion**: Among the given options, H2Te has the weakest E-H bond and the highest tendency to donate a proton, making it the strongest acid.

### Final Answer:
The strongest acid among the given options is **H2Te** (option number 4).

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