Answer : The density of a sample of chlorine gas is, 12.59 g/L
Explanation :
To calculate the density of chlorine gas we are using ideal gas equation.

where,
P = pressure of chlorine gas = 4.5 atm
V = volume of chlorine gas = 12.6 L
n = number of moles of chlorine gas
w = mass of chlorine gas
R = gas constant = 0.0821 L.atm/mol.K
T = temperature of chlorine gas = 
M = molar mass of chlorine gas = 71 g/mol
Now put all the given values in the above formula, we get:



Therefore, the density of a sample of chlorine gas is, 12.59 g/L