1. He met the boy in the classroom.

2. He shook hands with the boy in the classroom.
3. He talked with the boy in the classroom.
4. He observed the boy in the classroom.
5. He looked at the boy in the classroom.
.................
In each sentence,isn't 'in the classroom' an adverbial phrase' to modify each verb?

I don't think so.

https://en.wikipedia.org/wiki/Adverbial_phrase

Yes, you are correct. In each of the given sentences, the phrase "in the classroom" functions as an adverbial phrase. An adverbial phrase modifies verbs by providing additional information about where the action took place.

To determine if "in the classroom" is an adverbial phrase, you can ask yourself the question "where did the action happen?" In this case, the answer is "in the classroom," which indicates the location where the action described by the verb took place.

Let's break down each sentence to further understand how "in the classroom" serves as an adverbial phrase modifying the verb:

1. "He met the boy in the classroom."
- The verb is "met," which describes the action of meeting.
- The adverbial phrase "in the classroom" answers the question "where did he meet the boy?" and provides additional information about the location of the action.

2. "He shook hands with the boy in the classroom."
- The verb is "shook hands," which describes the action of shaking hands.
- The adverbial phrase "in the classroom" answers the question "where did he shake hands with the boy?" and provides information about the location of the action.

3. "He talked with the boy in the classroom."
- The verb is "talked," which describes the action of speaking.
- The adverbial phrase "in the classroom" answers the question "where did he talk with the boy?" and specifies the location of the action.

4. "He observed the boy in the classroom."
- The verb is "observed," which describes the action of observing.
- The adverbial phrase "in the classroom" answers the question "where did he observe the boy?" and provides information about the location of the action.

5. "He looked at the boy in the classroom."
- The verb is "looked at," which describes the action of looking.
- The adverbial phrase "in the classroom" answers the question "where did he look at the boy?" and specifies the location of the action.

In summary, "in the classroom" serves as an adverbial phrase in each of the given sentences by modifying the verb and providing information about the location of the action.