**Core Concept**
Newborn infants are administered vitamin K at birth to prevent vitamin K deficiency bleeding (VKDB), a type of bleeding disorder that can occur due to the newborn's inability to produce sufficient vitamin K. Vitamin K is essential for the production of clotting factors in the liver.

**Why the Correct Answer is Right**
Vitamin K is administered to newborns because they lack the intestinal bacteria that produce vitamin K, and their liver is not yet able to produce sufficient amounts. The recommended dose of vitamin K at birth is 1 mg intramuscularly. This dose helps to rapidly increase the newborn's vitamin K levels and prevent VKDB. The American Academy of Pediatrics recommends vitamin K administration at birth to all newborns.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the dose is too low and may not provide adequate protection against VKDB.
**Option B:** Incorrect because the dose is too high and may cause adverse effects such as bleeding or bruising.
**Option C:** Incorrect because the route of administration is incorrect; vitamin K should be administered intramuscularly, not orally.

**Clinical Pearl / High-Yield Fact**
It is essential to administer vitamin K at birth to prevent VKDB, which can cause severe bleeding and even death. Newborns who are at high risk for VKDB, such as those born to mothers with bleeding disorders or those who are premature, may require additional doses of vitamin K.

**Correct Answer: D. 1 mg intramuscularly.**