What property of a solution causes an acid–base indicator to change to different colors?

it can be used to predict atomic behavior in most circumstances.
it has been perfected and will never be changed in the future.
it is only accepted by a small fraction of scientists.
it is only useful in very specific circumstances.

The most common method to get an idea about the pH of solution is to use an acid base indicator. An indicator is a large organic molecule that works somewhat like a " color dye". Whereas most dyes do not change color with the amount of acid or base present, there are many molecules, known as acid - base indicators , which do respond to a change in the hydrogen ion concentration. Most of the indicators are themselves weak acids.

Determine the  wavelength of light emitted when an electron  in an li2+ ion  makes a transition from an orbital with n  =  6 to an orbital with n  = 5.