Can I replace my old charger with a new charger for free

If it is under warranty and failed through no fault of yours, probably yes.

If not, no.

If it got broken in an accident, such as dropping it, or water damage, no.

can I claim a replacement charger for my I pad air which is not charging properly.

Make an appointment at an Apple Store, take the items with you for an evaluation and see what they say. If the charger is still under warranty, they should replace it if it is found to be defective.