Question

question 1 of 10
the ph indicator bromothymol blue is blue in an alkaline solution and yellow in an acidic solution. a slight increase in acidity, such as when co₂ gas is added, causes a solution with the indicator to change from blue to yellow.
a solution with the indicator would be most likely to turn from yellow to blue when which combination of factors exists?

a. a person blows air into the solution through a straw.

b. algae are placed in the solution and left in a dark room.

c. water plants in the solution are placed under a bright lamp.

d. yeast cells and sugar are placed in the solution.

Explanation:

To determine when the solution turns from yellow (acidic) to blue (alkaline), we need a process that reduces acidity (or increases alkalinity). Photosynthesis by plants consumes \(CO_2\) (which makes solutions acidic) and produces \(O_2\), reducing acidity.

• Option A: Blowing air (containing \(CO_2\)) increases acidity (more \(CO_2\) dissolves, forming acid), so solution stays yellow or becomes more yellow.
• Option B: Algae in dark do respiration (produce \(CO_2\)), increasing acidity (more yellow).
• Option C: Water plants under bright light do photosynthesis, consuming \(CO_2\). This reduces the amount of acid - forming \(CO_2\) in the solution, increasing pH (making it alkaline), so the indicator turns blue.
• Option D: Yeast and sugar: yeast respires (produces \(CO_2\)), increasing acidity (more yellow).

Answer:

C. Water plants in the solution are placed under a bright lamp.