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.
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A calibration curve requires the preparation of a set of known concentrations of CV, which are usually prepared by dieting a stock solution whose concentration is known.
Answer:
A balanced equation demonstrates the conservation of mass by having the same number of each type of atom on both sides of the arrow.
