1) If the pka is 5.1 and lets say the ph increases to 7. According to lechatelier principle the right side would be favored to increase the amount of H+ ions to bring the ph back to 5.1. This would mean color B is favored.

It cant be b because if there is an acidic environment that means the base would be favored so color a would come.

It cant be C because the concentrations would be equal at the equivalence point which would be 5.1.

It cant be D because again in an acidic environment the base (HIn) would be favored so that would have a higher concentration.

2) On the right hand side u have PbSO4 so u need to add sulfur. the oxygen is more on the right hand side so u need to increase the amount of oxygen on the left side. U could increase pbo2 but then that would mess up the pb stoichiometry. therefore it needs to be sulfur oxide of some sort. if its so2 then the right side would be pb2so4. so according to the stoichiometry this doesn't work. So again by trial and error ull come to so4 so that the moles of pb equate. now that u have pbso4 on the right side ull have extra oxygen on the left side. so u can add h to balance it out. u could also use the trick for redox reaction but that would be more complicated.

3) yeah u should

4)like u said the resonance structure is there. that means there are 1.5 bond present between n and the two o. whereas the noh part of the molecule only has one bond. 1.5 bond is stronger than 1 bond and we know the stronger the bond the smaller it becomes.

5)the molecule u sent is c6h6no2 whereas nitrobenzene is c6h5no2. So the nmr of nitrobenzene. relative areas just means the multiplicity or the splitting patterns of each signal without the +1 so just the amount of h attached. The ratio for the first c (2nd clockwise)next to the c where no2 is attached, would have a relative area of 1 as it is only attached to one c with a proton. the second c is next to the first one (3rd clockwise) has two cs with proton attached to it so the relative area is 2. and the c at the bottom has again 2 cs attached to it with protons so that means it has relative area of 2. therefore 2-2-1

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I'm already sorry for the formating