What is the pressure exerted by 1.2 mol of a gas with a temperature of 20.°c and a volume of 9.5 l?

Let's assume that the gas is an ideal gas. Then we can use ideal gas equation,
PV = nRT
Where, 
P = Pressure of the gas (Pa)
V = volume of the gas (m³)
n = number of moles (mol)
R = Universal gas constant (8.314 J mol⁻¹ K⁻¹)
T = temperature in Kelvin (K)

The given data for the gas is,
P = ?
V = 9.5 L = 9.5 x 10⁻³ m³
T = (273 + 20) K = 293 K
R = 8.314 J mol⁻¹ K⁻¹
n = 1.2 mol

by applying the formula,
P x 9.5 x 10⁻³ m³ = 1.2 mol x 8.314 J mol⁻¹ K⁻¹ x 293 K
                        P = 307705.5 Pa
                        P =3.08 x 10⁵ Pa

Hence, the pressure of the gas is 3.08 x 10⁵ Pa.