Phospholipids make up most of the lipid part of the cell membrane. since water exists on both the outside and inside of a cell, which of the following phospholipid arrangements makes the most sense? a single layer of phospholipids with the polar heads facing outside the celltwo back-to-back phospholipid layers with the non-polar tails facing out on both sidesa single layer of phospholipids with the polar heads facing inside the celltwo back-to-back phospholipid layers with the polar heads facing out on both sides

Two back-to-back phospholipid layers with the polar heads facing out on both sides

Explanation:

Phospholipids are made up of a head  and two tails. The head can be described as a phosphate molecule that is water loving (hydrophilic) whereas fatty acids make up the two tails. The fatty acids repel water and hence are hydrophobic. The assembling of the phospholipids for the the formation of cell membrane depends on these hydrophilic and hydrophobic properties. The assembling of the phospholipids is in two layers. The phosphate head face outwards on both sides to attract water and the tails tend to hide from the water molecules by being composed in the layers of the head. this assembling is termed as the "self-assembly".

the correct option is option d

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.