Q.4 Take three test-tubes. Fill each of them with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of CO₂ ?

Test-tube A will have the highest concentration of CO₂ because :

(1) Test-tube A will have a snail that expels out CO₂ into the tube. Living organisms use oxygen and release CO₂ during respiration.

(2) Since a plant is present in both test tubes B and C, the plant will inhale CO₂ to decrease CO₂ concentration.

(3) Thus, there will be less concentration of CO₂ in B and C test tubes.