**Question:** Inner ear fully developed at

A. Birth
B. Fetus (end of 2nd trimester)
C. Infancy
D. Childhood

**Core Concept:** Development of the inner ear is crucial for understanding its function and abnormalities that may occur. The inner ear is responsible for hearing and balance, and its development is a crucial process during fetal life.

**Why the Correct Answer is Right:** The inner ear fully develops during the fetal stage, mainly in the end of the second trimester. This is when the hair cells, cochlea, and vestibular system reach their full maturity, ensuring proper hearing and balance functions postnatally.

**Why Each Wrong Option is Incorrect:**

A. Birth: Although the inner ear starts to develop around the 16th week of gestation, it is not fully developed at birth. Newborns may experience hearing and balance problems due to incomplete development.
B. Infancy: Although the inner ear structure continues to mature during infancy, the key components are fully developed at the end of the second trimester, making option B incorrect.
C. Infancy: Similar to option B, the inner ear is not fully developed during infancy, making it an incorrect choice.
D. Childhood: While the inner ear may undergo some structural maturation during childhood, the key components are fully developed during the fetal stage, making option D incorrect.

**Clinical Pearl:** Understanding the developmental timeline of the inner ear is crucial for diagnosing and managing hearing and balance disorders in newborns and infants. Delayed or absent development can lead to conditions like neonatal hearing loss and vestibular dysfunction, necessitating proper evaluation and treatment.

**Correct Answer:** B. Fetus (end of 2nd trimester)