During expiration,the diaphragm becomes

Select the correct statement.

What happens when the pressure within the pulmonary cavity is higher than the atmospheric pressure?

The thoracic cavity increases in volume primarily due to the contraction of which of the following?

Choose the correct option:
$(1)$ The volume of gases involved in breathing movements is measured by $Sphygmomanometer / Spirometer$.
$(2)$ Inspiration is initiated by the $relaxation / contraction$ of the diaphragm.

Inspiration occurs when intra-pulmonary pressure is