Assertion. In case of polyprotic acids, first ionization constant in lowest.
Reason. The removal of first proton is most difficult. Further ionization becomes easier.

Options

A. If both assertion and reason are true, and reason is the true explanation of the assertion.
B. If both assertion and reason are true, but reason is not the true explanation of the assertion.
C. If aasertion is true, but reason is false.
D. If both assertion and reason are false.

Explanation

To analyze the assertion and reason provided in the question, we can break it down step by step.

### Step 1: Understanding Polyprotic Acids
Polyprotic acids are acids that can donate more than one proton (H⁺) per molecule. Common examples include sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), and carbonic acid (H₂CO₃).

### Step 2: Ionization Constants
For polyprotic acids, each proton removal corresponds to a different ionization constant (K₁, K₂, K₃, etc.). The first ionization constant (K₁) is associated with the removal of the first proton, the second ionization constant (K₂) with the removal of the second proton, and so on.

### Step 3: Comparing Ionization Constants
In general, the first ionization constant (K₁) is lower than the subsequent constants (K₂, K₃) for polyprotic acids. This indicates that the first proton is removed less readily compared to the subsequent protons.

### Step 4: Difficulty of Proton Removal
The assertion states that the first ionization constant is the lowest. The reason provided states that the removal of the first proton is the most difficult, which is true. This is because the remaining species after the first proton is removed is often negatively charged, making it less favorable to remove another proton due to increased electrostatic repulsion.

### Step 5: Conclusion
Both the assertion and the reason are correct. The assertion that the first ionization constant is the lowest is supported by the reason that the removal of the first proton is indeed the most difficult.

### Final Answer
- **Assertion**: True - In case of polyprotic acids, the first ionization constant is the lowest.
- **Reason**: True - The removal of the first proton is the most difficult, making further ionization easier.