The best answer is D.
A. The
Phlogiston Theory, because the red powder resembled an ash
Incorrect. The formation of a new substance when a metal is heated in air is not
unique to the
Phlogiston Theory, it is also part of the Oxygen Theory, so the
formation of a powder resembling
ash would not support the Phlogiston Theory.
B. The
Phlogiston Theory, because the air in the reservoir could not support combustion
and therefore
did not contain oxygen
Incorrect. Combustion is not the process being tested by the experiment, and
the
results show that the metal is transformed in the experiment, so this reasoning
is not valid.
C. The
Oxygen Theory, because the mercury level dropped in the air reservoir indicating
increased oxygen content
Incorrect. The item states that the volume of mercury in the air reservoir,
which would be measured by the
level (or height) of mercury in the air
reservoir, increased, so this reason conflicts with the results.
D. The
Oxygen Theory, because the mercury level rose in the air reservoir indicating
decreased oxygen content
Correct. If the Oxygen Theory is accurate, the mercury will react with oxygen in
the air, forming calx (the red powder).
This will cause the air to decrease in
volume relative to the atmosphere, making the volume (and, therefore, the
height)
of mercury in the air reservoir increase.