Which of the following statements are correct ?
(i) `Ca^(+2)` is necessary for blood coagulation
(ii) Coagulation in blood vessel is prevented during normal condition by heparin
(iii) Clotting of blood involves changes of fibrinogen to fibrin by thrombin
(iv) Blood clotting involves casecading process involving a number of factors present always in the active form.

Options

A. (i),(iii) and (iv)
B. (ii) and (iv)
C. (i),(ii) and (iii)
D. (iii) and (iv)

Explanation

To determine which statements about blood coagulation are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement (i): `Ca^(+2)` is necessary for blood coagulation.**
- **Analysis:** Calcium ions (Ca²⁺) play a crucial role in the blood coagulation process. They are essential for the activation of several clotting factors and help in the conversion of prothrombin to thrombin, which is necessary for the formation of fibrin from fibrinogen.
- **Conclusion:** This statement is **correct**.

2. **Statement (ii): Coagulation in blood vessels is prevented during normal conditions by heparin.**
- **Analysis:** Heparin is an anticoagulant that is naturally present in the body. It is secreted by mast cells and prevents the clotting of blood within blood vessels, allowing for smooth blood flow.
- **Conclusion:** This statement is **correct**.

3. **Statement (iii): Clotting of blood involves changes of fibrinogen to fibrin by thrombin.**
- **Analysis:** Fibrinogen is a soluble plasma protein that is converted into insoluble fibrin by the enzyme thrombin during the coagulation process. This fibrin forms a mesh that helps to stabilize the blood clot.
- **Conclusion:** This statement is **correct**.

4. **Statement (iv): Blood clotting involves a cascading process involving a number of factors present always in the active form.**
- **Analysis:** The blood clotting process is indeed a cascading mechanism; however, the clotting factors are not always in the active form. They are typically present in an inactive form and become activated in response to injury or other stimuli.
- **Conclusion:** This statement is **incorrect**.

### Final Conclusion:
The correct statements are (i), (ii), and (iii). Therefore, the answer is that statements **(i), (ii), and (iii) are correct**.