Yes, you are correct. When carbon dioxide (CO2) is bubbled into bromothymol blue, the observed color change is from a blue-green color to yellow. The change in color indicates a change in pH.
Bromothymol blue is a pH indicator that changes color depending on the pH of the solution. It is blue at a basic pH, green at a neutral pH, and yellow at an acidic pH. When carbon dioxide is bubbled into bromothymol blue, it forms carbonic acid (H2CO3) in water, which increases the acidity of the solution and causes the color to change to yellow.
Therefore, the correct answer is indeed option a. "the color of the solution changed from greenish to yellow color." However, it is important to note that different sources may describe the initial color as greenish or blue-green.
It's great that you paid attention to the specific color change you observed, as it may vary depending on the exact concentration of bromothymol blue and the amount of carbon dioxide introduced.