1. A group of students help the sick.

Question

2. A group of students helps the sick.

(What is the difference between the two sentence? If both are grammatical, aren the following correct as well? )

3. This is a group of students.
4. These are a group of students.
5. These students are a group of
strong students.
6. Look at the students who are a
group of strong people.

Answer 1

#2 is correct. #1 is incorrect.
The word "group" is the subject and it's singular; therefore, you need the singular form of the verb -- "helps."

#3 is correct.

#4 is incorrect.

#5 is correct; the word "students" (plural) is the subject.

#6 is correct.