The pressure will double.

Explanation:

This is a direct application of the ideal gas law:

* PV = nRT

Where:

* P = Pressure

* V = Volume

* n = Number of moles

* R = Ideal gas constant

* T = Temperature

Since the volume (V) and temperature (T) are constant, we can simplify the equation to:

* P ∝ n (Pressure is directly proportional to the number of moles)

If you double the number of moles (n), you will double the pressure (P).