When a good indicator has been chosen, the pH at which the solution changes color is very close to the

equivalience point of the titration.

If this "point" for a particular titration occurs at pH x, a good indicator for the titration would be indicator.
X indicator
0.9 ?
1.5 ?
3.5 ?
6.1 ?
8.9 ?

What's the question?

the rest of the question asks: what is the indicator when X= 1.5, 3.5, 6.1, 8.9?

To determine the appropriate indicators for the given pH values, we need to find indicators that have a color change close to those pH values. Indicators are organic compounds that exhibit different colors in acidic and alkaline solutions.

When choosing an indicator, we want to select one that changes color as close as possible to the pH at the equivalence point of the titration. The equivalence point is the point at which the reactants have stoichiometrically reacted, indicating the completion of the reaction.

Let's look at the given pH values and find suitable indicators:

- For pH 0.9: The indicator that changes color close to this pH is methyl orange (pH range: 3.1-4.4).
- For pH 1.5: The indicator that changes color close to this pH is methyl orange (pH range: 3.1-4.4).
- For pH 3.5: The indicator that changes color close to this pH is bromothymol blue (pH range: 6.0-7.6).
- For pH 6.1: The indicator that changes color close to this pH is bromothymol blue or bromo cresol green (pH range: 6.0-7.6 for bromothymol blue, 3.8-5.4 for bromo cresol green).
- For pH 8.9: The indicator that changes color close to this pH is phenolphthalein (pH range: 8.2-10.0).

Therefore, we can suggest the following indicators for the given pH values:
- For pH 0.9: Methyl orange
- For pH 1.5: Methyl orange
- For pH 3.5: Bromothymol blue
- For pH 6.1: Bromothymol blue or Bromo cresol green
- For pH 8.9: Phenolphthalein