Two gases spread easily through each other because of their low density and high kinetic energy. The particles of a gas are widely spaced apart, and they move very quickly and randomly. This means that they collide with each other and with the walls of their container very frequently. When a gas particle collides with another gas particle, it changes direction and speed. This means that the particles of a gas are constantly moving in different directions, and they spread out over a large volume.

The density of a gas is also a factor in how easily it spreads. The density of a gas is the mass of the gas per unit volume. The lower the density of a gas, the more easily it will spread. This is because the lighter the molecules of a gas are, the more easily they can be moved by collisions with other molecules.

The kinetic energy of a gas is also a factor in how easily it spreads. The kinetic energy of a gas is the energy of motion of the gas particles. The higher the kinetic energy of a gas, the more easily it will spread. This is because the faster the molecules of a gas are moving, the more likely they are to collide with other molecules and change direction.

In summary, two gases spread easily through each other because of their low density and high kinetic energy. The particles of a gas are widely spaced apart and move rapidly, which means that they collide with each other and the walls of their container frequently. This constant motion causes the gases to spread out over a large volume.