GAZ as someone who scored 100% in the actual test, a little advice. There is variation in 'correctness' throughout. Some answers are not 'wrong' it is just a case that another is more correct. This is what can drive people slightly crazy, you have studied, you know the core material, it's still possible to select the 'wrong' answer (even if it isn't wrong as such). There are various question banks on the net, some helpful others not vary in content and correctness.
I recommend the PPL Confuser to sort out which is the CAA 'correct' answer and an explanation of why it is 'correct'. Use with caution though, learn from the books first, but makes sure you have a good look through the Confuser explanations before sitting a test. It will save you a lot of frustration.
As an explanation of one of your examples:
4. What is displayed on the altimeter when QNH is set on the subscale?
A. Zero
B. Sea level
C. Airfield elevation
D. Transition altitude
The PPL book says: when QNH is set on the subscale, the altimeter reads altitude above mean sea level (AMSL). I find the question terminology very confusing, because isnt the correct answer actually none of the above? Wouldn't the correct answer actually be: 'altitude above mean sea level'?
Here the correct answer is C. Airfield elevation. Why? Because the aircraft is sat on the ground and if you set QNH whilst sat on the ground and the airfield has an elevation of 300' amsl, then that is what will be shown by the altimeter, 300'. IF you set QFE it would read Zero.
The PPL Confuser is helpful not because it just gives you the correct answers, but rather it explains why they are correct for the given question.