Solubility of iodine in water may be increased by adding

The solubility of $CO_2$ in water increases with

The oxygen dissolved in water exerts a partial pressure of $20 \ kPa$ in the vapour above water. The molar solubility of oxygen in water is ............ $\times 10^{-5} \ mol \ dm^{-3}$ (Round off to the Nearest Integer). [Given: Henry's law constant $K_H = 8.0 \times 10^{4} \ kPa$ for $O_2$,Density of water $= 1.0 \ kg \ dm^{-3}$]

What is the solubility of a gas in water at $25^{\circ} C$ if the partial pressure is $0.346 \ bar$ (Henry's law constant is $0.159 \ mol \ dm^{-3} \ bar^{-1}$)?

If $O_2$ gas is bubbled through water at $303 \; K$,the number of millimoles of $O_2$ gas that dissolve in $1 \; L$ of water is (Nearest Integer). (Given: Henry's Law constant for $O_2$ at $303 \; K$ is $46.82 \; kbar$ and partial pressure of $O_2 = 0.920 \; bar$). (Assume solubility of $O_2$ in water is too small,nearly negligible).

What is the significance of Henry's Law constant $K_H$?