When 0.01 mole of ammonia is dissolved in sufficient water to make 1 litre of solution, the solution is found to have a hydroxide ion concentration of 1.3.1 - 6. The dissociation constant of ammonia is:
A) 1.3.1 - 6
B) 0.01
C) 1.3.1 + 6
D) 1.3