Why do apples turn brown?

1. Does soaking them in salt water help to prevent them from turning brown for a period of time?

2. Is it bad for our health if we eat apples that have turned brown?

3. Does only apples turn brown when in contact with air or do other fruits also turn brown?

3.1. New node

3.2. New node

4. Does soaking them in a solution of sugar and water prevent them from turning brown for a period of time?

5. If we leave cut apples in contact with the air for a longer time, do they turn more brown?