Acidic Strength of Compounds:

The acidic strength of a compound is determined by its ability to donate a proton (H+ ion) in an aqueous solution. The compound that donates a proton most easily is considered to be the strongest acid.

Order of Acidic Strength:

The correct order of acidic strength among the given compounds is:

a) Cl2O7 < so2="" />< />

Let's analyze each compound and understand their acidic strengths:

1. Cl2O7 (Dichlorine heptoxide):
- It is an acidic oxide that reacts with water to form an acid (HClO4).
- The acidic strength of Cl2O7 is determined by the electronegativity and size of the central atom (Cl).
- In Cl2O7, the central Cl atom is highly electronegative and large in size, which makes it difficult to attract and stabilize the resulting negative charge after donating a proton.
- Therefore, Cl2O7 is the weakest acid among the given compounds.

2. SO2 (Sulfur dioxide):
- It is a gas formed by the combustion of sulfur or sulfide minerals.
- SO2 can act as an acid by reacting with water to form sulfurous acid (H2SO3).
- The acidic strength of SO2 is determined by the electronegativity and size of the central atom (S).
- In SO2, the central S atom is less electronegative and smaller in size compared to Cl in Cl2O7.
- The smaller size of the S atom allows it to attract and stabilize the resulting negative charge more effectively, making SO2 a stronger acid than Cl2O7.

3. P4O10 (Phosphorus pentoxide):
- It is a white solid formed by the reaction of phosphorus with excess oxygen.
- P4O10 can react with water to form phosphoric acid (H3PO4).
- The acidic strength of P4O10 is determined by the electronegativity and size of the central atom (P).
- In P4O10, the central P atom is less electronegative and larger in size compared to S in SO2.
- The larger size of the P atom allows it to attract and stabilize the resulting negative charge even more effectively than S, making P4O10 the strongest acid among the given compounds.

Conclusion:

Based on the analysis, the correct order of acidic strength among the given compounds is: Cl2O7 < so2="" />< p4o10.="" />