The normal intrapleural pressure at the start/beginning of inspiration is ………………………………. cm of H20
–7.5
–5.0
–2.0
–0.5
The intrapleural pressure becomes more negative at the end of inspiration and less negative at expiration. 
It ranges between -3 and -6 mmHg. At the beginning of inspiration, the pressure is -3.8mmHg (-5 cm of water), and at the end of inspiration (beginning of expiration), it is -6mmHg ( -8 cm of water). 
The elasticity of lung and rib cage causes it to recoil and thus creating the negative pressure. 
The lymphatic drainage of the pleural fluid also creates a negative pressure.