Final answer:
In CPR, an adult's chest should be compressed at least 2 inches deep to effectively circulate blood and maintain oxygen delivery to vital organs like the brain.
Step-by-step explanation:
The correct answer to how far down you should compress an adult's chest during CPR is at least 2 inches (5 cm). This level of compression is necessary to ensure that the blood within the heart is manually compressed enough to be pushed into the pulmonary and systemic circuits. Performing high-quality chest compressions at a rate of 100 compressions per minute, comparable to the beat of 'Staying Alive' by the Bee Gees, is crucial for maintaining blood flow, especially to the brain, to prevent irreversible damage.