Attached to this thread is the question and mark scheme.
The Attempt at a Solution
I got most of the question right but I have no idea about the explanation part of why to include the 100 ohm resistor which is required for the higher level. It says in the mark scheme about the fact that the LED gets 2V across it when points A-B get 6V. I have no idea how we know this? To know the LED gets 2V requires knowing its resistance which we don't know? Unless its related to the graph in the first part of the question but it says that is for a silicon diode. Also if it did relate to question in first part then 2V according to the graph would have much less than 50 ohms resistance