How to delete a Play store accpunt through system I have sold my old android mobile to a person and made sure that the mobile was completely formatted.

But, when I try to view the list of devices in Play Store it is listing both my new and old mobile phones.

Is it possible to remove this old phone from the list so that the other person doesn't use my account?
If you performed a /data wipe (factory reset) on your old phone, you have nothing to worry about; that person will not be able to "automatically" log onto your Google Account. Old phones will always show up on Play Store when you're looking from your PC.

You cannot remove the device from Play Store, but you can hide it from your Google Play Settings from a PC. Just untick Show in menus next to the device you want to hide.