1. She also takes the sick chilren outside in wheelchairs/ a wheelchair.

2. She took the patient in a wheelchair.

3. She took the sick person in wheerchairs.

(Which expressio do I have to use? A singular form or a plular form:a wheelchair or wheelchairs? Are the expressions above grammatical?)

Wheelchair has to agree with the number of persons you are taking out.

children more than one - wheelchairs

patient = one - wheelchair.

All three expressions can be grammatically correct depending on the context. Let's break it down:

1. "She also takes the sick children outside in wheelchairs."
This implies that there are multiple sick children, and each child is taken outside in their own wheelchair. Here, "wheelchairs" is used in the plural form to match the multiple children.

2. "She took the patient in a wheelchair."
Here, the sentence suggests that there is a single patient being taken in a single wheelchair. Thus, "a wheelchair" is used in the singular form.

3. "She took the sick person in wheelchairs."
In this case, the expression is not grammatically correct. Since it refers to a single sick person, it should be "She took the sick person in a wheelchair" using the singular form.

To choose between singular or plural forms, consider whether you are referring to one wheelchair or multiple wheelchairs, and whether the action involves one person or multiple people.