Given a K_b value of 1.5 x 10^-5 for a weak base, calculate the K_a of its conjugate acid at 25°C.

• A. K_a = 6.7 x 10^-9
• B. K_a = 6.7 x 10^-7
• C. K_a = 6.7 x 10^-8
• D. K_a = 6.7 x 10^-10

Answer: (D)