SPOT THE ERROR:First I could not recognize but later I realized that he was the friend of my father's.

Explanation

"Father's" is incorrect in its current form. The phrase "the friend of my father's" should be "a friend of my father's" to avoid redundancy. The possessive should not follow the definite article "the." There is an error hereThe error in the sentence is the phrase "the friend of my father's." The correct form should be "a friend of my father's" to properly convey possession without redundancy. Thus, the correct option to mark the error is D) Father's.