**Core Concept**
The question is testing the knowledge of skeletal maturity and its assessment in children. The Greulich-Pyle (G-P) atlas is a widely used method for estimating the skeletal age of children, which helps in assessing their growth and development.

**Why the Correct Answer is Right**
The best X-ray to determine the age of a 12-year-old child is the hand and wrist radiograph, specifically the left hand, as it is a reliable indicator of skeletal maturity. The G-P atlas correlates the X-ray findings of the left hand and wrist with the corresponding age ranges. The X-ray is taken with the hand in a specific position, and the ossification centers, epiphyseal plates, and carpal bone ages are assessed to estimate the child's skeletal age. This information is essential in pediatric endocrinology and orthopedics for diagnosing conditions like growth hormone deficiency or delayed puberty.

**Why Each Wrong Option is Incorrect**
**Option A:** An AP (anteroposterior) view of the lumbar spine is not a reliable method for determining skeletal age in children, as it may not accurately reflect the overall skeletal maturity.

**Option B:** A chest X-ray is not suitable for assessing skeletal age, as it does not provide information about the ossification centers, epiphyseal plates, or carpal bone ages.

**Option C:** A lateral view of the spine is not a reliable method for determining skeletal age, as it may not accurately reflect the overall skeletal maturity.

**Clinical Pearl / High-Yield Fact**
The G-P atlas is a widely used reference for estimating skeletal age, but it is essential to remember that it is not a definitive method and should be used in conjunction with other clinical and laboratory findings to make a diagnosis.

**Correct Answer:** B. Hand and wrist radiograph.