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.
In comparison with liquids and gases, solids are more dense. The answer is letter B. <span>The
solid has a more definite shape and volume. The particles are locked into
place. It cannot be further compressed due to the bond that exists between the
molecules. The kinetic energy of the molecules is close to none because the
molecules are so close and so compact with each other. </span>