You would want to make sure that you have controlled the variables properly, and if you determine that you did then you would repeat the experiment to be sure of the results.
Answer: The correct option is (c). The total pressure doubles.
Solution:
Initially, only 4 moles of oxygen gas were present in the flask.
(
) ( according to Dalton's law of partial pressure)
....(1)
= Total pressure when only oxygen gas was present.
Final total pressure when 4 moles of helium gas were added:

partial pressure of oxygen in the mixture :
Since, the number of moles of oxygen remains the same, the partial pressure of oxygen will also remain the same in the mixture.

= Total pressure of the mixture.
from (1)

On rearranging, we get:

The new total pressure will be twice of initial total pressure.
Answer:
we only see parts of the lit side as the moon goes around the earth
Explanation:
Unlike the sun, the moon orbits the Earth. This is the reason why we see the <em>different phases of the moon.</em> The reflection of the moon is being illuminated back to us with the help of the sun. So, as the moon circles the Earth, we only see parts of the lit side. Such changes helps us see the moon in different phases such as<em> </em>the <em>Third Quarter, Crescent, New Moon, Full Moon, etc.</em>
For example, during "Full Moon," <em>the moon's entire face is lit up by the sun</em>. Thus, we see the entire moon's lit portion.
Thus, this explains the answer.