I can tell you're not very educated because everyone knows that breathing pure oxygen for long periods of time can sometimes hurt us. Oxygen in lower levels, such as levels found in atmosphere are just right for us to breathe. Get a life and stop trying to scare young kids that just want help on their homework.
A solution is turning blue means, it is turning it's behavior to Basic from Acidic. Reagent D must be a Basic component so it is increasing the pH of the solution. As reaction does not depend on the phase of the component, it could be anything i.e., Solid, Liquid or gas.
Hope this helps!
The charge for this compound is positive. For Fe, it's charge is positive 3, and for OH, it's charge is negative 1. You would then criss cross the charges of each and come out with Fe(OH)3. I hope this helped!! :)
