answers, confirmed with my entire grade, including those ranked higher than me:
1. D - it is not B (which I put stupidly) and the rest are clearly wrong because ozone is not even in those layers
2. A - lowest locant must be on "bromo" and then "fluoro" not the other way around.
3. B - by elimination, Arrhenius was hydrogen ions, Davy was hydrogen and Lavoisier was oxygen
4. C - by elimination, A is clearly wrong, B is not cracking it is polymerisation, D is not breaking up larger hydrocarbons
5. C - by elimination, A & B are both wrong as there is not double bond in the reactant, D is wrong as well
6. B - (not exactly sure, please confirm), because all values are the lowest except for dissolved oxygen which is good. D is wrong
7. C - by elimination, D is wrong because ammonia is pink in phenolphthalein, and A & B are wrong because they are not yellow in methyl red.
8. B - make sure to note temperature decrease, ph goes up, therefore [H+] goes down. D is wrong because think it about the chemistry of ionisation.
9. A - because Y can't be an isomer with any of the other options eliminating B, C and D
10. C - because either H2O and OH- are paired or HOCl and OCl- are paired. C is the later the rest are wrong.
11. A (I put C, C is wrong because A is not a coordinate covalent bond)
12. C - A & B are wrong, pH is a logarithmic scale, and also D is wrong it is [H+] you are after.
13. B (I put A) - A is wrong because it should dip up, C & D are clearly wrong. The vertical line is all substances change that much.
14. D - use the formula makesure to include the negative
15. D - convert each to moles, the most moles of substance is the biggest i.e. D. All the reactions are 1:1.
16. B - check the oxidation numbers for A & D it goes up, for C it doesn't change, therefore B is correct
17. A - chromate is reduced, and SO2 is oxidised therefore A. Not B because the oxidiation potential of SO2 is not 0.16 but -0.16
18. D - compare the structures, A to C are all inconsistent with the diagram given above.
19. B - calculation
20. D - can't be A or C because think Haber process exothermic reaction, lower temperature better. as pressure goes up, shifts to the right, i.e. side with less molecules, therefore B is wrong.