Data:
C1 (initial concentration) = 7.5 g/L
P1 (initial pressure) = 404 kPa
C2 (final concentration) = ? (g/L)
P2 (final pressure) = 202 kPa
We apply the data to the formula of the solubility of gases in a liquid (Henry's Law), let us see:
\(\boxed{ \dfrac{C_1}{P_1} = \dfrac{C_2}{P_2}}\)
Solving:
\(\dfrac{7.5}{404} = \dfrac{C_2}{202}\)
\(404*C_2 = 7.5*202\)
\(404C_2 = 1515\)
\(C_2 = \dfrac{1515}{404}\)
\(\boxed{\boxed{C_2 = 3,75\:g/L}}\end{array}}\qquad\checkmark\)
I hope this helps. =)
