Final answer:
The antecubital fossa is the preferred site for initiating IV access in an older adult client because the median cubital vein is easily accessible there and is commonly used for venipuncture.
Step-by-step explanation:
When initiating IV access for an older adult client, the preferred site is typically one that presents the least risk for complications and provides easy access for the healthcare provider. In this case, the median cubital vein, which is a superficial vessel located in the antecubital fossa region and links the cephalic vein to the basilic vein, is often chosen. This vein is a frequent site for venipuncture due to its accessibility and size, making it a suitable option for initiating an IV in an older adult. Therefore, the correct answer to the student's question is: b) Antecubital fossa.