Charles law gives the relationship between volume and temperature of gas at constant pressure
it states that at constant pressure, volume of gas is directly proportional to temperature
V/T = k
where V - volume T - temperature and k - constant

parameters for the first instance are on the left side of the equation and parameters for the second instance are on the right side of the equation
T1 - temperature in Kelvin - 27 °C + 273 = 300 K
T2 - 11 °C + 273 = 284 K
substituting the values in the equation
2.6 L / 300 K = V / 284 K
V = 2.46 L
New volume of the gas is 2.46 L
There are TWO atoms in one molecule of hydrogen.
pV = nRT
p = nRT/V
p= 1 x 0.08205 x 1000/ 2
p = 41.025 Pa
Edit: The unit should be atm instead of Pa, as pointed out by a nice human being.