The Following Pictures Represent Solutions That Contain a Weak Acid

Multiple Choice

The following pictures represent solutions that contain a weak acid HA and/or its potassium salt KA.Unshaded spheres represent H atoms and shaded spheres represent A^- ions.(K⁺,H₃O⁺,OH^-,and solvent H₂O molecules have been omitted for clarity. )
-For which solution(s) is pH = pK_a?

A) only solution (1)
B) only solution (2)
C) only solution (3)
D) solutions (1) and (3)