The correct option is B (b)
Let’s examine the sentence: “I was disappointed when I came for seeing you last evening but could not find you at home.” The phrasal verb “to see” and not “for seeing” is used to express the fact of visiting and meeting someone at any point in time. Hence, the correct version of the sentence would be, “I was disappointed when I came to see you last evening but could not find you at home.” So, the error is in Part b of the sentence. Hence, Option B is the correct answer.