Calculate the Amount of Ammonium Chloride (NH₄Cl) That Must Be

Calculate the amount of ammonium chloride (NH₄Cl) that must be added to 1.0 L of 0.10 M NH₃ ( K _b = 1.8×10 ^{- 5}) to prepare a buffer of pH 9.00.

A) 0.10 mole
B) 0.056 mole
C) 0.18 mole
D) 5.6×10 ^{- 5} mole
E) buffer cannot be made