Layer food for adult chickens is not medicated. You only feed medicated food for chicks for the first 8 weeks. Then you switch over to Layer-Grower food. ( 16-18 % protein)
I assume your other chickens are adults ?
If your not sure of what kind of food you have, medicated or not, Do NOT feed the duckling that food. It should say on the bag .
Feed the duckling only NON-Medicated food.
It is very important to find out which feed you have on hand.
You can feed the duck oatmeal, cooked., bread crumbs...small pieces of peas, corn...
If the other duckling doesn't hatch, you can keep the duck with the other chickens, they will get along fine but not until the duckling is atleast 8 weeks old. otherwise, the chickens or roosters will bully the duck or even kill it. It's best to have atleast two ducks if your going to have ducks. the more, the merrier.
If you re-home the duck to the next door neighbors, that would be the best option but keep in mind that if the neighbors ducks are not locked up at night, you will almost definately loose that duckling to predators. I NEVER let my ducks free range without supervision. Hawks, Owls, Coyotes, possoms, wild dogs, Racoons will hunt them down and kill them. I learned the hard way. My animals are in lock-down at night.
If you decide to keep the duckling, buy a couple more and build a seperate coop for them. I have 12 ducks and I have a ball with them. They are so much fun to have....and require very little care....Good Luck.
...And the duckling you have is definately a Pekin. They are great layers and beautiful ducks.