Final answer:
The correct answer is option d. In an aqueous solution of the weak acid H₂C₂O₄ at equilibrium, the species are present in the following order from highest to lowest concentration: H₂C₂O₄ > H₃O+ > HC₂O₄⁻ > C₂O₄⁸⁸, which corresponds to option 'd'. This order reflects the extent of dissociation of the diprotic acid.
Step-by-step explanation:
The student is asking about the concentrations of different species in an aqueous solution of the weak acid oxalic acid (H₂C₂O₄) at equilibrium. The correct order, from highest to lowest concentration, will be determined by considering the degree of dissociation of the acid.
Oxalic acid is a diprotic acid, which means it can donate two protons (H+ ions). The first dissociation is usually stronger than the second. So, initially, H₂C₂O₄ will dissociate to form HC₂O₄⁻ and H₃O+, and then HC₂O₄⁻ can dissociate further to form C₂O₄⁸⁸ and another H₃O+. However, the second dissociation is weaker than the first, which means there will be more HC₂O₄⁻ than C₂O₄⁸⁸, and both will be less than H₂C₂O₄. Therefore, the concentration of H₃O+ will be higher than that of C₂O₄⁸⁸ because the H₃O+ comes from two dissociation steps.
Thus, considering the equilibrium in a solution of a weak diprotic acid, the correct order from highest to lowest concentration at equilibrium will be:
H₂C₂O₄ > H₃O+ > HC₂O₄⁻ > C₂O₄⁸⁸. This corresponds to option 'd' among the choices provided. The species with the highest concentration is the undissociated weak acid H₂C₂O₄, followed by the hydronium ion (H₃O+), then the singly deprotonated form (HC₂O₄⁻), and lastly the fully deprotonated form (C₂O₄⁸⁸).