Final answer:
The ultrasound probe for a supraclavicular block should be placed posterior to the clavicle, in the supraclavicular fossa.
Step-by-step explanation:
The correct placement of the ultrasound probe for a supraclavicular block is posterior to the clavicle, in the supraclavicular fossa. This is because the supraclavicular block targets the brachial plexus, which is located in the supraclavicular fossa. Placing the probe in this position allows for accurate visualization of the target area and ensures effective administration of the block.