Step 1: Understanding the process of water absorption.
Water absorption by root hairs occurs in three distinct stages:
Imbibition: This is the initial stage where water is absorbed by hydrophilic substances (e.g., cell wall components like cellulose) through capillary action.
Diffusion: After imbibition, water molecules diffuse from regions of higher concentration (soil solution) to lower concentration (root hair cells).
Osmosis: Finally, water moves through the semipermeable membranes of root hair cells into the root cortex via osmotic gradients.
Step 2: Explanation of the correct sequence.
The correct sequence in water absorption is:
\[
\text{Imbibition} \rightarrow \text{Diffusion} \rightarrow \text{Osmosis}.
\]
Imbibition occurs first as the cell walls absorb water.
Diffusion facilitates water movement to the root hair cytoplasm.
Osmosis enables water transport across membranes into deeper root cells.
Step 3: Explanation of other options.
Option (B): Incorrect. Osmosis does not occur first; imbibition precedes it.
Option (C): Incorrect. Diffusion does not occur before imbibition.
Option (D): Incorrect. Osmosis occurs after diffusion, not before.
\[
\therefore \text{The correct sequence is: Imbibition, diffusion, osmosis.}
\]