The correct option is B 10−10
The equilibrium reaction is as shown below.
Fe(OH)2⇌Fe2++2OH−
The equilibrium constant is K=Ka1×ka2=1×10−4×2.5×10−4=2.5×10−10
The expression for the equilibrium constant =K=[Fe2+][OH−]2[Fe(OH)2]
Substitute values in the above expression, we get
2.5×10−10=(0.1−x)(1.0×10−7−2x)2x
On solving this equation, we get x=1×10−10