Question

choose the molecule that is most concentrated at each ph. ph = 4 ph = 7 ph = 10

Explanation:

Step1: Observe pH = 4 on graph

At pH = 4, the red - colored curve representing $H_2CO_3$ is at the highest position among the three curves, meaning it has the highest concentration.

Step2: Observe pH = 7 on graph

At pH = 7, the purple - colored curve representing $HCO_3^-$ is at the highest position among the three curves, indicating it has the highest concentration.

Step3: Observe pH = 10 on graph

At pH = 10, the blue - colored curve representing $CO_3^{2 - }$ is at the highest position among the three curves, so it has the highest concentration.

Answer:

pH = 4: $H_2CO_3$
pH = 7: $HCO_3^-$
pH = 10: $CO_3^{2 - }$