A sample of ascorbic acid (vitamin C) is synthesised in the laboratory. It contains 1.50 g of carbon and 2.00 g of oxygen. Another sample of ascorbic acid isolated from citrus fruits contains 6.35 g of carbon. How many grams of oxygen does it contain? Which law do you assume in answering this question?

Options

A. 7.25 : Law of conservation of mass
B. 6.35 : Law of definite proportions
C. 8.47 : Law of definite proportions
D. 6.35 : Law of multiple proportions

Explanation

To solve the problem, we need to determine how many grams of oxygen are present in the second sample of ascorbic acid, given the amount of carbon it contains. We will use the Law of Definite Proportions for this calculation.

### Step-by-Step Solution:

1. **Identify the Mass of Carbon and Oxygen in the First Sample:**
- In the first sample of ascorbic acid, we have:
- Mass of Carbon (C) = 1.50 g
- Mass of Oxygen (O) = 2.00 g

2. **Calculate the Ratio of Carbon to Oxygen:**
- To find the ratio of carbon to oxygen in the first sample, we can set up the following ratio:
\[ \text{Ratio of C to O} = \frac{\text{Mass of C}}{\text{Mass of O}} = \frac{1.50 \, \text{g}}{2.00 \, \text{g}} = 0.75 \]

3. **Identify the Mass of Carbon in the Second Sample:**
- In the second sample of ascorbic acid, we have:
- Mass of Carbon (C) = 6.35 g

4. **Set Up the Proportion Using the Law of Definite Proportions:**
- According to the Law of Definite Proportions, the ratio of the masses of carbon and oxygen should remain constant. Therefore, we can set up the following equation:
\[ \frac{6.35 \, \text{g C}}{x \, \text{g O}} = \frac{1.50 \, \text{g C}}{2.00 \, \text{g O}} \]
- Here, \( x \) is the mass of oxygen we want to find.

5. **Cross-Multiply to Solve for \( x \):**
- Cross-multiplying gives us:
\[ 6.35 \, \text{g C} \times 2.00 \, \text{g O} = 1.50 \, \text{g C} \times x \, \text{g O} \]
- This simplifies to:
\[ 12.70 = 1.50x \]

6. **Solve for \( x \):**
- Dividing both sides by 1.50 gives:
\[ x = \frac{12.70}{1.50} \approx 8.47 \, \text{g O} \]

### Final Answer:
The second sample of ascorbic acid contains approximately **8.47 grams of oxygen**.