Question

why lungs always contain a residual volume of air.

Answer 1

so that there is sufficient time to absorb oxygen nd release carbon dioxide

Answer 2

$\huge\mathfrak\red{Heya\:Mate}$

$\huge{\boxed{\bold{ANSWER}}}$

During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbondioxide to be released.

$\large{\bold{HOPE \:IT \:HELPS \:YOU!!!}}$