An element A ( at. wt . = 75) and B( at. wt . =25) combine to form a compound. The compund contain 75% A by weight. The formula of the compound will be

Options

A. AB
B. `AB_(3)`
C. `A_(3)B`
D. `A_(2)B`

Explanation

To determine the formula of the compound formed by elements A and B, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Data:**
- Atomic weight of element A = 75
- Atomic weight of element B = 25
- The compound contains 75% A by weight.

2. **Calculate the Percentage of B:**
- Since the compound contains 75% A, the percentage of B will be:
\[ \text{Percentage of B} = 100\% - 75\% = 25\% \]

3. **Assume a Total Mass of the Compound:**
- For simplicity, assume the total mass of the compound is 100 grams. This makes calculations straightforward.
- Mass of A in the compound = 75 grams (75% of 100 grams)
- Mass of B in the compound = 25 grams (25% of 100 grams)

4. **Calculate the Number of Moles of Each Element:**
- Moles of A:
\[ \text{Moles of A} = \frac{\text{Mass of A}}{\text{Atomic weight of A}} = \frac{75 \text{ g}}{75 \text{ g/mol}} = 1 \text{ mole} \]
- Moles of B:
\[ \text{Moles of B} = \frac{\text{Mass of B}}{\text{Atomic weight of B}} = \frac{25 \text{ g}}{25 \text{ g/mol}} = 1 \text{ mole} \]

5. **Determine the Simplest Ratio:**
- The ratio of moles of A to moles of B is:
\[ \text{Ratio} = \frac{1 \text{ mole of A}}{1 \text{ mole of B}} = 1:1 \]

6. **Write the Empirical Formula:**
- Since the ratio of moles of A to B is 1:1, the empirical formula of the compound is:
\[ \text{Empirical Formula} = AB \]

### Final Answer:
The formula of the compound is **AB**.

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