The presence of carbon dioxide (CO2) is an important factor to consider in respiration experiments. In these experiments, potassium hydroxide (KOH) is commonly used to absorb the carbon dioxide released during respiration. However, if one forgets to keep the vial with KOH in the conical flask, it will result in a variation in the outcome of the experiment. Let's delve into the details of how the result may vary in such a scenario.

1. Lack of CO2 Absorption:
- If the vial with KOH is not present in the conical flask, there will be no CO2 absorption happening in the experiment.
- Without the absorption of CO2, the released gas will remain in the conical flask, leading to an increase in the concentration of CO2 within the flask.

2. Increased Carbon Dioxide Concentration:
- As the respiration process continues, the concentration of CO2 in the conical flask will progressively rise.
- The increased concentration of CO2 will result in a change in the color of the indicator used in the experiment.
- For example, if bromothymol blue is used as an indicator, it will turn yellow in the presence of excess CO2.

3. Altered pH Level:
- The increased concentration of CO2 will lead to the formation of carbonic acid (H2CO3) when it reacts with water in the conical flask.
- The formation of carbonic acid will decrease the pH level of the solution, making it more acidic.
- The change in pH is an indication of the accumulation of CO2 and the absence of CO2 absorption.

4. Inaccurate Measurement of Respiration Rate:
- The purpose of using KOH in the conical flask is to absorb the released CO2, which allows for accurate measurement of the respiration rate.
- Without the absorption of CO2, the measured respiration rate will be higher than the actual rate since all the released CO2 is not being accounted for.
- This can lead to misleading or inaccurate results in the experiment.

In conclusion, if one forgets to keep the vial with KOH in the conical flask during an experiment where CO2 is released during respiration, the result will vary significantly. The absence of CO2 absorption will lead to an increased concentration of CO2, altered pH level, and inaccurate measurement of the respiration rate. It is crucial to ensure the presence of KOH to achieve reliable and accurate results in respiration experiments.