1. We did cardiopulmonary resuscitation to the wouded.

Question

2. We gave first aid to the injured.

(Are they both grammatical? Do we have to use 'to'? What does 'the wounded' and 'the injured' mean? Singular or plural? Thank you.)

Answer 1

Both are grammatically correct.

The wounded and the injured both mean people who have been hurt. As nouns, they are both plural.