we are going to use Henry's law:
when C1/P1 = C2/P2
at a constant temperature.
and when the C1 and C2 are the concentration of the gases ( the solubility)
and P1 and P2 is the Pressure 1 and pressure 2
and when 760 mmHg = 1 atm
so, by substitution:
1.6 g/L / 1 atm = C2 /2.5 atm
∴C2 = 1.6g/L *2.5atm /1 atm
= 4 g/L