Where is the default ringtone stored? I recently brought a Sony Xperia C. One of my friends like a few default ringtones of the phone. I tried to search in the internal as well as sd card memory but couldn't find the ringtone.

Where exactly they are stored? Can I send it to my friends using another android phone?
Default ringtones are usually stored in /system/media/audio/ringtones. You might be able to access this location using a file manager.

Keep in mind that, residing on /system, this place is read-only at best without root-access: so while you should be able to copy from here, you cannot place any files into this directory. If you want to manually add ringtones to your device, rather create a similar directory on your SDcard (/sdcard/media/audio, with sub-directories for ringtones, alarms, notifications, etc.). This location should be recognized automatically by the Android system.