I have seen that moodle dev team has had problems in introducing neg marks. To work around this I tried to introduce an option for each and every answer namely "I dont know" which will be given a higher mark than a wrong answer.
But the problem is:
How do I have this option "I dont know" pre-selected for each and every question. In other words how does one have each question already have a pre- selected option to it. This will ensure that if students even if they are not able to complete the test should have the pre selected option ("I dont know") for every question.
If even this is not possible, please suggest some work around this negative marking problem cause its absolutely critical for my application.