Hydrazine, N₂H₄, Is a Weak Molecular Base with a Value

Hydrazine, N₂H₄, is a weak molecular base with a value of 9.6 × 10^-7 for K_b. An aqueous solution contains 0.200 M N₂H₄ and 0.376 M N₂H₅Cl per liter as the only solutes. If the K_sp of Fe(OH) ₂ is 7.9 × 10^-16, what is the maximum [Fe²⁺] that can coexist with these solutes in the solution? Hint: Use the Henderson-Hasselbalch formula to find the pOH of the solution, then use that to find [OH^-].

A) 1.5 × 10^-9 M
B) 4.1 × 10^-9 M
C) 0.00024 M
D) 0.00086 M
E) 0.0030 M