Tab Order Issue with Radio Buttons

Typically, after tabbing to a radio button, you use the up and down arrow keys to move through the button set, with the "current" button being selected. Then you use the tab key to move to the next element (e.g., the Submit button).

• See https://access.articulate.com/support/article/Storyline-Navigate-Multiple-Choice-Questions-with-a-Screen-Reader-or-Keyboard 

Because your radio buttons have triggers to show feedback layers, that functionality is overridden. Using an arrow key selects the next radio button, which immediately opens the associated layer. So you need to switch to programming with a separate button to submit the answer.

You could have saved yourself some effort by using a graded question slide. Consider converting the existing slide to a Freeform Pick One, and then use the default Submit button, or create a custom one.