The direction of gas movement is determined by solubility of the gas in blood size of the gas molecule temperature ph partial pressure differences

The direction of gas movement is determined by Partial Pressure Difference.

Explanation:
                   According to phenomenon of Diffusion and Effusion gases always move from level of higher concentration to level of lower concentration. In lungs the oxygen moves from external atmosphere to inner body due to difference in partial pressure of Oxygen. Oxygen present in higher quantity outside body moves in through alveoli. And CO₂ present in body moves out through lungs. Same process takes place at tissue level.

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na