Acidic order of following compounds is :
(I) `H_(2)O_(2)," (II)" H_(2)O,`
(III) `H_(2)," (IV)"D_(2)O`

Options

A. I gt II gt III gt IV
B. II gt I gt IV gt III
C. IV gt I gt II gt III
D. I gt II gt IV gt III

Explanation

To determine the acidic order of the compounds \( H_2O_2 \) (hydrogen peroxide), \( H_2O \) (water), \( H_2 \) (hydrogen), and \( D_2O \) (deuterium oxide), we need to analyze the factors that influence acidity. The two major factors affecting acidity are:

1. The size of the atom bonded to hydrogen.
2. The electronegativity of the atom bonded to hydrogen.

### Step-by-Step Solution:

**Step 1: Analyze the compounds**
- **Hydrogen Peroxide (\( H_2O_2 \))**: Contains two oxygen atoms, which are highly electronegative and relatively large in size.
- **Water (\( H_2O \))**: Contains one oxygen atom, which is also electronegative and has a bent structure.
- **Hydrogen (\( H_2 \))**: Consists of two hydrogen atoms. It does not have any electronegative atoms bonded to it, making it the least acidic.
- **Deuterium Oxide (\( D_2O \))**: Similar to water but contains deuterium instead of hydrogen. Deuterium is slightly heavier than hydrogen but does not significantly affect acidity.

**Step 2: Compare Acidity**
- **\( H_2O_2 \)**: The presence of two electronegative oxygen atoms makes it more acidic than water.
- **\( H_2O \)**: More acidic than \( D_2O \) because oxygen is more electronegative than deuterium.
- **\( D_2O \)**: Slightly less acidic than water due to the presence of deuterium.
- **\( H_2 \)**: The least acidic because it lacks electronegative atoms.

**Step 3: Establish the order**
Based on the analysis, the acidic order from strongest to weakest is:
1. \( H_2O_2 \) (most acidic)
2. \( H_2O \)
3. \( D_2O \)
4. \( H_2 \) (least acidic)

Thus, the final acidic order is:
\[ H_2O_2 > H_2O > D_2O > H_2 \]

### Conclusion
The acidic order of the compounds is:
\[ (I) H_2O_2 > (II) H_2O > (IV) D_2O > (III) H_2 \]