1. Convert Temperature to Kelvin:

* T(K) = T(°C) + 273.15

* T(K) = 28°C + 273.15 = 301.15 K

2. Use the Ideal Gas Law to Find Moles of HCl:

* PV = nRT

* P = Pressure (atm) = 2.61 atm

* V = Volume (L) = 2.14 L

* n = Moles (mol)

* R = Ideal Gas Constant = 0.0821 L*atm/mol*K

* T = Temperature (K) = 301.15 K

* Rearrange the equation to solve for n:

* n = PV / RT

* n = (2.61 atm * 2.14 L) / (0.0821 L*atm/mol*K * 301.15 K)

* n ≈ 0.223 mol HCl

3. Calculate the Molarity:

* Molarity (M) = Moles of solute / Liters of solution

* Moles of solute = 0.223 mol HCl

* Liters of solution = 668 mL = 0.668 L (remember to convert mL to L)

* M = 0.223 mol HCl / 0.668 L

* M ≈ 0.334 M

Therefore, the molarity of the hydrochloric acid solution is approximately 0.334 M.