In slide#3, the triggers on my check button ain't working. The check button (when clicked) should show me the correct/incorrect window depending upon the drag and drop results + it should stop the audio. The audio does stop if you click on it but the other two task are getting skipped for god knows what reason. If anyone can please help me out?
Ah! Good question. The Submit button - along with other Slide Navigation controls - can be turned on or off via the Slide Properties window for the Base layer. To access the Slide Properties window, select the Base layer, then click the gear icon at the bottom right-hand of your screen.
As you may know, the reason SL provided you a Submit button is due to your use of a Drag & Drop freeform question slide (or converting your existing slide into a D&D freeform question slide). The standard D&D slide works great when you're OK using the default Drop Correct and Drop Incorrect states and Submit button...however, when you want to add a new custom state and trigger the feedback via a custom button (as you did with "Dropped" and the "Check" button), then I would suggest not starting with SL D&D slide (or converting to a D&D slide). Instead, follow an approach like the one I demonstrated to account for those custom elements.
I was able to resolve your issue by introducing variables for each answer choice and having SL focus on showing the CORRECT layer if all the variables were TRUE, and showing the INCORRECT layer if any of the variables were not true.