Experts please explain....

Dear Student,

The value of water potential is calculated as :

Water potential = Solute potential + Pressure Potential

where, solute potential is determined by the concentration of salt in water and pressure potential value is equivalent to Hydrostatic pressure determined relative to atmospheric pressure.
When a solution is maintained at atmospheric pressure the pressure potential is nullified due to no hydrostatic pressure at atmospheric pressure.

Hence, the equation now would read as 

Water potential = Solute potential + 0
Resulting in,

 Water potential = Solute potential
Hence, option B is correct.

Regards