Final answer:
The last obstacle climbers encounter on Mount Everest is the Hillary Step, a vertical rock face near the summit, combined with harsh conditions like extreme cold and low oxygen.
Step-by-step explanation:
The last obstacle on the way to the summit of Mount Everest is known as the Hillary Step, a nearly vertical rock face at 28,750 feet, just below the summit. However, it's worth noting that the notorious feature has been altered in recent years, possibly by the 2015 earthquake in Nepal. Climbers heading for the summit must also face extreme conditions such as extreme cold, low oxygen levels, and low barometric pressure, which make any final ascent challenging and potentially hazardous.