Ais a protein that faces the outer surface of a cell and binds to hormones or other chemical messengers.
a. storage protein
b. messenger protein
c. transport protein
d. receptor

The correct answer is option D, Receptor protein

Explanation:

A Receptor protein is found on the outer side of the cell and they provide receptor sites where a foreign chemical messenger can get associated and perform its function.  As the name also suggest , “receptor” which receives chemical signals from outside a cell. Some common example of receptor proteins are ion channels such as ligand gated ion channels , enzymes etc.

Thus,  it can be a receptor protein which has the ability to bind to hormones or other chemical messengers.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.