The most abundant elements by mass in the body of a healthy human adult are: Oxygen (61.4%), Carbon (22.9%), Hydrogen (10.0%), and Nitrogen (2.6%). The weight which a 75 kg person would gain if all `.^(1)H` atoms are replaced by `.^(2)H` atoms is:

Options

A. 10 kg
B. 15 kg
C. 37.5 kg
D. 7.5 kg

Explanation

To solve the problem, we will follow these steps:

### Step 1: Determine the mass of hydrogen in a 75 kg person.
Given that hydrogen constitutes 10% of the body mass, we can calculate the mass of hydrogen in a 75 kg person.

\[ \text{Mass of } H_1 = \frac{10}{100} \times 75 \text{ kg} = 7.5 \text{ kg} \]

### Step 2: Calculate the mass of deuterium (H2).
Deuterium (H2) is an isotope of hydrogen that has double the mass of protium (H1). Therefore, the mass of H2 that would replace all H1 atoms can be calculated as follows:

\[ \text{Mass of } H_2 = 2 \times \text{Mass of } H_1 = 2 \times 7.5 \text{ kg} = 15 \text{ kg} \]

### Step 3: Calculate the increase in weight.
To find the increase in weight when all H1 atoms are replaced by H2 atoms, we subtract the original mass of hydrogen from the mass of deuterium:

\[ \text{Increase in weight} = \text{Mass of } H_2 - \text{Mass of } H_1 = 15 \text{ kg} - 7.5 \text{ kg} = 7.5 \text{ kg} \]

### Conclusion:
If all H1 atoms in a 75 kg person are replaced by H2 atoms, the person would gain 7.5 kg.

### Final Answer:
The weight gained by the person is **7.5 kg**.

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