Answer
See the answer below.
Work Step by Step
a) From Henry's law:
$S=k_HP$
$S=1.3\times10^{-3}mol/kg.bar\times1.5\ atm\times1.013\ bar/atm=0.002\ mol/kg$
b) By Henry's Law, raising the partial pressure of O2 increases its solubility in water, therefore its dissolved concentration will increase. When the pressure of O2 is reduced, the solubility decreases and so does the concentration of dissolved O2.
