Asample of 0.0200 mol of chlorine gas is kept at 27.0°c and 0.150 atm. what would be its pressure if the temperature was increased to 227.°c and the volume kept the same

Answer is:  0,250 atm.
T₁(chlorine) = 27°C = 300K.
T₂(chlorine) = 227°C = 500K.
T₂/T₁ = 1,66.
p1(chlorine) = 0,150 atm.
p2(chlorine) = ?
V(chlorine) = constant.
n(chlorine) = 0,0200 mol.
R - gas constant, R = 0.0821 atm·l/mol·K. 
Ideal gas law: p·V = n·R·T.
p = n·R·T÷V.
If temperature was increased 1,66 times, pressure also increase 1,66 times: 1,66·0,150 atm = 0,250 atm. 

The answer is c. valence electrons