How does the value of ka and kb compare with the concentrations of hydronium ion and hydroxide ion?
ka x kb= [h3o+][oh-]
ka x kb> [h3o+][oh-]
ka x kb< [h3o+]+[oh-]
ka x kb+ [h3o]/[oh-]

Assuming that we are given the values of Ka and Kb, these can be rewritten and represented by the concentration of the Hydronium ion and Hydroxide Ion:

Hydronium ion: [H3O+]
Hydroxide ion: [OH-]

Ka is the equilibrium constant of an acid which dissociates to a hydronium ion and its cation.
Kb is the equilibrium constant of a base which dissociates to a hydroxide ion and its anion. 

So,

Ka x Kb = [H3O+][OH-]

The correct answer is A, Ka × Kb = [H₃0⁺][OH⁻]

I hope this helps, have a good day and good luck! :)

Dsolubility let me know if you have any other questions for chemistry