Explain why copper(II) and iodide ions do not co-exist in acidic solution but do co-exist in the presence of ammonia. I want solution ASAP

A Cu electrode is immersed in a solution that is 1.00 M in [Cu(NH3)4]2+ and 1.00 M in NH3. When the cathode is a standard hydrogen electrode, the emf of the cell is found to be +0.08 V. What is the formation constant for[Cu(NH3)4]2+?

1.  A 0.9882 gram sample of iron ore is dissolved, the iron reduced to Fe2+, and the solution was titrated with 36.40 mL of 0.02065 M KMnO4 in acid solution. (a)  Write the titration reaction.  (b)  Calculate the %FeO (M.M. = 71.85) in the sample.   2.  A sample of primary standard grade K2Cr2O7 (MM = 294.20) weighing 0.2153 g is dissolved, the solution acidified and excess KI added. The liberated I2 requires 44.86 mL of the Na2S2O3 for titration. (a)  Write the titration reaction.  (b)  Calculate the molarity of the titrant solution.    Box the final answer.

Complete and balance the following half-reaction in acidic solution TiO₂ (s) → Ti²+ (aq) + O₂²(aq)