How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?
Neutral solutes move across the plasma membrane by the process of simple diffusion along the concentration gradient, i.e., from higher concentration to lower concentration. This movement occurs without any requirement of energy and is called passive transport.
No, polar molecules cannot move across the membrane in the same way. The polar molecules cannot pass through the nonpolar lipid bilayer of the membrane.
Polar molecules require a carrier protein of the membrane to facilitate their transport across the membrane. This is necessary because the nonpolar lipid bilayer does not allow polar molecules to pass through it freely.
Explanation
The textbook clearly explains that neutral solutes use simple diffusion (passive transport) along the concentration gradient without energy requirement. Polar molecules cannot pass through the nonpolar lipid bilayer and therefore require carrier proteins for facilitated transport across the membrane.