PV = nRT

Where:

* P is the pressure (in atmospheres, atm)

* V is the volume (in liters, L)

* n is the number of moles

* R is the ideal gas constant (0.0821 L·atm/mol·K)

* T is the temperature (in Kelvin, K)

1. Rearrange the equation to solve for pressure (P):

P = nRT / V

2. Plug in the given values:

* n = 0.683 mol

* R = 0.0821 L·atm/mol·K

* T = 326 K

* V = 20.1 L

3. Calculate the pressure:

P = (0.683 mol * 0.0821 L·atm/mol·K * 326 K) / 20.1 L

P ≈ 0.919 atm

Therefore, the pressure in the cylinder is approximately 0.919 atm.