Answers for "how to make radio button checked by default"

default checked radio button

<input type="radio" name="imgsel" value="" checked>

html radio button checked

<input type="radio" id="huey" name="drone" value="huey"
         checked> 
<!-- https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/radio-->

radio by default selected

checked="checked"