The most important buffer in the blood consist of :

Options

A. `HCl and Cl^(-)`
B. `H_(2)CO_(3) and H_(2)CO_(3)^(-)`
C. `H_(2)CO_(3) and Cl^(-)`
D. `HCl and HCO_(3)^(-)`

Explanation

To solve the question regarding the most important buffer in the blood, we can follow these steps:

### Step 1: Understand the concept of buffers
A buffer is a solution that resists changes in pH when small amounts of an acid or a base are added. Buffers are essential in biological systems, including blood, to maintain a stable pH.

### Step 2: Identify the components of blood buffer systems
The primary buffer system in blood consists of a weak acid and its conjugate base. In the case of blood, the two main components are carbonic acid (H2CO3) and bicarbonate ion (HCO3-).

### Step 3: Write down the chemical species involved
- **Carbonic Acid (H2CO3)**: This is the weak acid component of the buffer system.
- **Bicarbonate Ion (HCO3-)**: This is the conjugate base of carbonic acid.

### Step 4: State the pH range maintained by the buffer
The bicarbonate buffer system helps maintain the blood pH within a narrow range of approximately 7.35 to 7.45, which is crucial for proper physiological function.

### Step 5: Choose the correct answer from the options
Given the components identified, the most important buffer in the blood consists of:
- **H2CO3 (carbonic acid) and HCO3- (bicarbonate ion)**.

Thus, the correct answer is **H2CO3 and HCO3-**.

### Summary of the Solution
The most important buffer in the blood consists of carbonic acid (H2CO3) and bicarbonate ion (HCO3-), which work together to maintain the pH of blood within the range of 7.35 to 7.45.

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