The correct option is A 0.50 M
We know,
Molarity=moles of NaCltotal volume of solution (mL)×1000=0.25500×1000=0.5 M
Again,
NaCl→Na++Cl−
1 mole of NaCl dissociates to give 1 mole of Cl− ions,
Thus, 0.25 moles NaCl gives 0.25 moles of Cl− ions
Since number of moles of Cl− is same as NaCl, thus molarity of Cl− is also 0.5 M.