Assertion (A) : Osmotic behavior of plant cells depends on surrounding solution
Reason (R) : If external solution is hypertonic then plant cell undergo plasmolysis. If external solution is hypotonic plant cell become turgid.

Assertion (A) is correct. The osmotic behavior of plant cells, including their turgor pressure, is indeed influenced by the tonicity (hypertonic, isotonic, or hypotonic) of the surrounding solution. 
Reason (R) is also correct. When the external solution is hypertonic (having a higher solute concentration than the cell's cytoplasm), water will tend to move out of the plant cell. This loss of water causes the cell's central vacuole to shrink, and the cell undergoes plasmolysis. Plasmolysis is the process where the cell membrane pulls away from the cell wall, and the cell becomes flaccid. When the external solution is hypotonic (having a lower solute concentration than the cell's cytoplasm), water will tend to move into the plant cell. This influx of water increases the pressure within the cell, causing it to become turgid. Turgor pressure is the pressure exerted by the cell contents against the cell wall, and it is responsible for maintaining the cell's rigidity.
A and R correct, R explains A