1. This is a group of students who help the sick.

2. These are a group of students who help the sick.

3. This is a group of students who helps the sick.

4. These are a group of students who helps the sick.

(Which expressions are correct? Please focus on 'this' and 'help. Is 'group' a collective noun? Thank you.)

#3. This is singular as is group, a collective noun. The group it does help, is helping, helps.

These is plural so it would have to be "These groups"

Sra

1. This is a group of students who help the sick. OK

2. These are groups of students who help the sick.

3. This is a group of students who helps the sick. OK

4. These are groups of students who help the sick.

Out of the four given expressions, Option 1 and Option 3 are correct.

Explanation:

1. "This is a group of students who help the sick." - This expression is correct because it uses the singular form "this" to refer to a singular group. The verb "help" is in the plural form to agree with the plural noun "students" within the group.

2. "These are a group of students who help the sick." - This expression is not correct because it uses the plural form "these" to refer to a singular group. The correct form would be "This is a group."

3. "This is a group of students who helps the sick." - This expression is correct because it uses the singular form "this" to refer to a singular group. In this case, the verb "helps" is in the singular form because "group" is considered a collective noun, which can be treated as a singular entity.

4. "These are a group of students who helps the sick." - This expression is not correct because it uses the plural form "these" to refer to a singular group. The correct form would be "This is a group." Additionally, the verb "helps" should be in the plural form to agree with the plural noun "students" within the group.

To summarize, the correct expressions are Option 1: "This is a group of students who help the sick." and Option 3: "This is a group of students who helps the sick." Each utilizes the correct agreement between the pronoun "this," the verb "help/helps," and the noun "group."