How are lipid molecules arranged in the cell membrane?

What is the cell membrane composed of?

Singer and Nicholson's model of plasma membrane differs from Robertson's model in the

Who proposed the concept of the unit membrane?

For the cell membrane, the name "plasmalemma" was given by:

Monovalent ions (e.g.,$Na^+, K^+$) $A$ the membrane permeability,while divalent ions $B$ the same. Complete the given statement by filling in the appropriate option for ($A$ and $B$).