Question

what will happen if a rbc cell is kept in concented salt solution

Answer 1

It depends on what kind of salt solution you are using.

If the salt solution is hypotonic with respect to RBCs (that is salt solution is rarer in osmotically active particles than intracellular plasma) then the water molecules will osmosis into the RBCs from the solution and it might lead to rupturing of RBCs.

If the salt solution is hypertonic (opposite of hypotonicity) then the water molecules will osmosis out of the RBCs leading to plasmolysis (extensive shrinkage of RBCs due to hypertonic environment).

Answer 2

If the water potential inside the cell is higher than the solution (in the case of a conc. salt solution), water diffuses out of the cell making the cell flaccid (shrunken cytoplasm).