Final answer:
The correct answer is C. at the very bottom of the beaker
Step-by-step explanation:
According to the given information, the density of the steel nail is 8g/cm3, the density of water is 1g/cm3, and the density of mercury is 13.6g/cm3.
Since the density of the steel nail is greater than that of water, the nail will sink in water. However, the density of mercury is greater than that of the steel nail. Therefore, the nail will settle at the very bottom of the beaker, below both the water and the mercury.
Thus, the correct answer is C. at the very bottom of the beaker.