Does apple are replace an AirPod if you lose one

Nor for free. But it will replace one or both AirPods for a single fee.

Click here ➜AirPods Repair & Service - Apple Support

If you have AppleCare+, you pay only one incident fee to replace a single AirPod or both AirPods, with or without a Charging Case. For service covered by AppleCare+, your fee per incident will be the same regardless of which service provider you choose.

No

There is no warranty coverage for lost or stolen Airpods.

If you bought AppleCare plus, you can purchase a new one for a reduced fee.

AirPods Repair & Service - Apple Support