**Core Concept**
Vitamin B7, also known as biotin, is a water-soluble B-complex vitamin that plays a crucial role in energy metabolism. It acts as a coenzyme for several carboxylase enzymes involved in fatty acid synthesis, gluconeogenesis, and amino acid metabolism.

**Why the Correct Answer is Right**
Biotin is required for the synthesis of fatty acids from acetyl-CoA, a process that is essential for energy production. The recommended daily intake of biotin is not well established, but it is generally agreed that a diet containing 2-3 milligrams of biotin per day is sufficient to meet the body's needs. The requirement for biotin is often expressed in terms of energy expenditure, with a commonly cited estimate being 1 microgram of biotin per 100 kilocalories.

**Why Each Wrong Option is Incorrect**
**Option A:** Not a valid estimate of biotin requirement.
**Option B:** This option is not supported by scientific evidence.
**Option C:** Not a correct estimate of biotin requirement.

**Clinical Pearl / High-Yield Fact**
Biotin deficiency can lead to skin rash, hair loss, and neurological symptoms. It is often seen in individuals with malabsorption syndromes, such as celiac disease, or those taking long-term anticonvulsant medications.

**Correct Answer:** C. 2-3 micrograms.