How to make the radio field checked by default? I have a field group which consists of a radio box and other fields. This field group can have multiple values. My radio box field have two options and the first is checked by default. But when I add the second value (of the field group) – my radio field has no checked option, both options are empty (in the newly added field group). Is it possible to make the first checkbox option always checked?

Here's the short video showcasing the problem: https://www.dropbox.com/s/366xt4q57ryvteu/drupal-radio-issue.mp4?dl=0
I canno't comment to suggest you a solution, but it's probably due to the module field_group (or fieldgroup).

You should try the same content type configuration by using field_collection, because i have never faced any issue with this module.

1/ You create a new field type : field collection. You setup the field with an unlimited number of occurrences.

2/ You go to structure > field collection and add your fields.

I hope it help

Cheers.