True statements about vitamin K are: a) Increases the synthesis of factor II, VII, IX and X b) Require exposure to sunlight c) Causes hemolytic anemia in patients with G–6–PD deficiency d) t1/2 is < 6 hour

**Core Concept**
Vitamin K plays a critical role in the synthesis of certain clotting factors in the liver, which are essential for the coagulation cascade. It acts as a cofactor for the enzyme gamma-glutamyl carboxylase, enabling the carboxylation of glutamate residues in these proteins.

**Why the Correct Answer is Right**
Vitamin K is necessary for the production of factors II (prothrombin), VII, IX, and X, as well as proteins C and S, which are involved in the regulation of coagulation. These factors are synthesized in the liver and require vitamin K-dependent carboxylation to become functional. This process is vital for the prevention of bleeding disorders. The correct answer highlights the importance of vitamin K in the synthesis of these essential clotting factors.

**Why Each Wrong Option is Incorrect**
* **Option B:** Vitamin K is not directly related to exposure to sunlight. Instead, vitamin D is the vitamin that is synthesized in the skin upon exposure to sunlight.
* **Option C:** Vitamin K does not cause hemolytic anemia in patients with G-6-PD deficiency. It is actually fava beans, which contain a compound called vicine, that can trigger hemolytic anemia in individuals with this genetic disorder.
* **Option D:** The half-life (t1/2) of vitamin K is actually longer than 6 hours. Vitamin K1 (phylloquinone) has a half-life of around 48 hours, while vitamin K2 (menaquinone) has a half-life of up to 9 days.

**Clinical Pearl / High-Yield Fact**
Vitamin K deficiency can lead to bleeding disorders, including easy bruising and bleeding gums. This is because the lack of vitamin K impairs the production of functional clotting factors, making it challenging for the body to form blood clots.

**Correct Answer:** a) Increases the synthesis of factor II, VII, IX and X