If Expiratory Reserve Volume = a , Residual Volume = B , Tidal Volume = C and Inspiratory Reserve Volume = D, then Funtional Residual Capacity (FRC) is equal to

Options

A. A + B
B. A + B + C
C. B + D
D. A + B + D

Answer

To solve the question regarding the Functional Residual Capacity (FRC), we need to understand the definitions of the lung volumes provided in the question:

1. **Expiratory Reserve Volume (ERV)**: This is the amount of air that can be forcibly exhaled after the expiration of a normal tidal volume. In this case, it is denoted as **A**.

2. **Residual Volume (RV)**: This is the volume of air remaining in the lungs after a maximal exhalation. It is denoted as **B**.

3. **Tidal Volume (TV)**: This is the amount of air inhaled or exhaled during normal breathing. It is denoted as **C**.

4. **Inspiratory Reserve Volume (IRV)**: This is the amount of air that can be inhaled after a normal inhalation. It is denoted as **D**.

Now, the question asks for the Functional Residual Capacity (FRC), which is defined as the amount of air remaining in the lungs after a normal expiration.

### Step-by-Step Solution:

**Step 1: Understand the formula for FRC.**
- The Functional Residual Capacity (FRC) is calculated by adding the Residual Volume (RV) and the Expiratory Reserve Volume (ERV).

**Formula**:
\[ \text{FRC} = \text{RV} + \text{ERV} \]

**Step 2: Substitute the variables with their respective values.**
- From the question, we know:
- RV = B (Residual Volume)
- ERV = A (Expiratory Reserve Volume)

**Step 3: Write the equation with the substituted values.**
- Therefore, we can express FRC as:
\[ \text{FRC} = B + A \]

**Step 4: Rearrange the equation.**
- This can also be written as:
\[ \text{FRC} = A + B \]

### Final Answer:
Thus, the Functional Residual Capacity (FRC) is equal to \( A + B \).