Percentage of Normal dead space is:-

Dead space - Some of the air a person breathes never reaches the gas exchange areas but simply fills respiratory passages where gas exchange does not occur, such as the nose, pharynx & trachea. - The air is called 'dead space air' because its not useful for gas exchange. - Normal tidal volume = 500 m - Normal dead space = 150 m Thus, Normal dead space ratio = 30 - 40%