Two gas jars are connected to each other, but they are separated by a closed valve. one gas jar contains oxygen, and the other contains hydrogen. what will happen when the valve is opened?

Both gasses will diffuse into the other jar until the molecules are well distributed into both containers. Diffusion is the movement of molecules from a point of high concentration to areas of low concentration until equilibrium is attained.   The mixture of gases will have a partial pressure that is equal to the sum of the partial pressures of the component gases.

answer; /// i do believe that the correct answer is (a) boiling

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.