A. Chlorine is the most electronegative element out of the possible choices. Generally (though not 100% of the time) electronegativity increases as you go further left and up the periodic table.
Firstly we need to determine the partial pressure of O2:

We will now use the Henry's Law equation to determine the solubility of the gas:

Answer: Solubility is 2.7x10^-3 M
Answer: 600 mL
Explanation:
Given that;
M₁ = 5.85 m
M₂ = 1.95 m
V₁ = 200 mL
V₂ = ?
Now from the dilution law;
M₁V₁ = M₂V₂
so we substitute
5.85 × 200 = 1.95 × V₂
1170 = 1.95V₂
V₂ = 1170 / 1.95
V₂ = 600 mL
Therefore final volume is 600 mL