Insensible fluid loss refers to water lost through:
(a) perspiration only
(b) feces only
(c) perspiration and expiration
(d) urine and feces

C. Perspiration and expiration.

Explanation – Insensible water loss is the type of loss which can't be felt like loss through perspiration or sweat and evaporation loss from the respiratory tract which is expiration. Sensible water loss is mainly urine which is released under our senses like see, feel and measure.

Insensible water loss is around 500-650ml/day according to some sources. There are certain factor that affects insensible water loss and are : temperature of the environment, humidity, altitude etc.