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We need to find the process taking place in contraction of diaphragm.

When the diaphragm contracts and the rib cage expands, the thoracic cavity expands, causing the volume of the thoracic cavity to grow. When the thoracic cavity expands, the lungs' flexibility permits them to expand. According to Boyle's law, as the capacity of the lungs rises, the pressure inside the lungs drops, eventually falling below the atmospheric pressure. A pressure gradient exists between the lungs and the atmosphere due to this difference in pressures. Molecules flow from a higher pressure location to a lower pressure area in a pressure gradient. Air rushes into the lungs during the inhalation phase of breathing, known as inspiration, until the pressure within the lungs equals the pressure in the environment.

We need to find the process takes place when the volume of lungs decreases.

The thoracic cavity's volume shrinks, which squeezes the lungs and reduces their volume. Expiration occurs when the pressure in the lungs exceeds the pressure in the environment, causing air to flow out of the lungs.

We need to find the process which takes place when pressure in lungs is less than that of atmosphere.

According to Boyle's law, as the capacity of the lungs rises, the pressure inside the lungs drops, eventually falling below the atmospheric pressure. A pressure gradient exists between the lungs and the atmosphere due to this difference in pressures. Molecules flow from a higher pressure location to a lower pressure area in a pressure gradient. Air rushes into the lungs during the inhalation phase of breathing, known as inspiration, until the pressure within the lungs equals the pressure in the environment.