Let's analyze the given statements regarding dithionite ($\text{S}_2\text{O}_4^{2-}$) and dithionate ($\text{S}_2\text{O}_6^{2-}$) anions to determine which ones are correct.

Understanding Dithionite and Dithionate

Dithionite anion has the chemical formula $\text{S}_2\text{O}_4^{2-}$. Its structure contains an S-S bond. The two sulfur atoms are bonded to two oxygen atoms each, with some resonance structures involving double bonds.

Dithionate anion has the chemical formula $\text{S}_2\text{O}_6^{2-}$. Its structure also contains an S-S bond, with each sulfur atom bonded to three oxygen atoms.

Analyzing Statement A: Presence of S-S Bond

• For dithionite ($\text{S}_2\text{O}_4^{2-}$), the structure is $\text{O}_2\text{S-SO}_2^{2-}$ (simplified representation showing the S-S link). There is a direct bond between the two sulfur atoms.
• For dithionate ($\text{S}_2\text{O}_6^{2-}$), the structure is $\text{O}_3\text{S-SO}_3^{2-}$. There is also a direct bond between the two sulfur atoms.

Thus, statement (A) which says both have an S−S bond is correct.

Analyzing Statement B: Dianionic Nature

• The formula for dithionite is $\text{S}_2\text{O}_4^{2-}$. The superscript indicates a net charge of -2. This means it is a dianionic species.
• The formula for dithionate is $\text{S}_2\text{O}_6^{2-}$. The superscript indicates a net charge of -2. This also means it is a dianionic species.

Thus, statement (B) which says both are dianionic is correct.

Analyzing Statement C: Oxidation States of Sulphur

We can calculate the oxidation state of sulfur in each anion:

• For dithionite ($\text{S}_2\text{O}_4^{2-}$): Let the oxidation state of sulfur be $x$. The oxidation state of oxygen is typically -2. The total charge is -2. $2x + 4(-2) = -2$ $2x - 8 = -2$ $2x = -2 + 8$ $2x = 6$ $x = +3$ The oxidation state of sulfur in dithionite is +3.
• For dithionate ($\text{S}_2\text{O}_6^{2-}$): Let the oxidation state of sulfur be $y$. The oxidation state of oxygen is typically -2. The total charge is -2. $2y + 6(-2) = -2$ $2y - 12 = -2$ $2y = -2 + 12$ $2y = 10$ $y = +5$ The oxidation state of sulfur in dithionate is +5.

Statement (C) says the oxidation state of sulfur is +3 and +5, respectively (for dithionite and dithionate). This matches our calculations, so statement (C) is correct.

Analyzing Statement D: Lone Pairs in Dithionate

Let's consider the structure of dithionate ($\text{S}_2\text{O}_6^{2-}$), which is $\text{O}_3\text{S-SO}_3^{2-}$. Each sulfur atom is bonded to one other sulfur atom and three oxygen atoms. The oxidation state of sulfur is +5. Sulfur is in Group 16 and has 6 valence electrons. In an oxidation state of +5, sulphur has effectively lost 5 valence electrons. The remaining valence electron from each sulfur is used to form the S-S bond. The bonding to the three oxygen atoms involves the other 5 valence electrons of each sulfur atom. For example, in a structure like $\text{O}_3\text{S-}$, the sulphur forms bonds with three oxygens (and one S). A resonance hybrid involves structures where sulfur forms one single S-S bond, one single S-O bond (with negative formal charge on O), and two double S=O bonds. In such structures, sulfur uses all 6 of its valence electrons in bonding (1 to S, 1 to O, 4 to 2 O's). Therefore, there are no lone pairs on the sulfur atom in dithionate.

Thus, statement (D) which says sulfur in dithionate has lone pair of electrons is incorrect.

Conclusion

Based on the analysis:

• Statement (A) is correct.
• Statement (B) is correct.
• Statement (C) is correct.
• Statement (D) is incorrect.

The correct statements are A, B, and C.