The letter that indicates the portion of the molecule that would be exposed to the aqueous environment is D.
What is the letter?
Suppose this molecule was incorporated into a cell membrane, the letter that indicates the portion of the molecule that would be exposed to the aqueous environment is letter D, the hydrophilic region.
We can identify the hydrophilic region of a phospholipid as its head, also known as the polar head. This head is made up of a phosphate group (PO₄²⁻) and sometimes an additional small group attached to a glycerol backbone. It is the part that would face outside.