Which ions in flint water caused the protective layer inside the pipes to break down?

The answer is Oxygen ions & Chloride ions.  Although Dissolved Oxygen (DO) can not interact with the Lead, Orthophosphates have to be added continually or the barrier breaks down. If the barrier does break down, DO combines with Lead atoms, oxidizing them. It allows Lead to drain into drinking water. Once oxidized, Lead dissolves into the water instead of sticking to the pipe. Flint’s water treatment plant did not add
orthophosphates,  allowing the pipes to corrode, and Lead quickly contaminated the drinking water. Additionally, Flint River water had high levels of chlorides, which accelerate corrosion.

Ithink 2 is the correct

Hbr dissociates to form h+ and br-ca(oh)2 dissociates to form ca2+ and 2oh-the h+ and oh- react to form waterassuming the reactants are dissolved in water, the net reaction is h+ + oh- —> h2oif you’re asked to show all components of the reaction, the complete reaction is 2hbr + ca(oh)2 —> cabr2 + 2h2o