The p-Block Elements (Group 15 to 18)

$H_2S_2O_8$, peroxodisulphuric acid: Two S-OH, Four S=O, One S-O-O-S $H_2SO_3$, sulphurous acid: Two S-OH, One S=O bond $H_2S_2O_7$, pyrosulphuric acid: Two S-OH, Four S=O, One S-O-S bond $H_2SO_4$, sulphuric acid: Two S-OH, Two S=O

ICl is more reactive than $I_2$ because the I–Cl bond is polar and weaker than the I–I bond. In general, the X–X' bond in interhalogens is weaker than the X–X bond (except F–F). So both A and R are correct and R is the correct explanation of A.

From $H_2S$ to $H_2Te$, boiling point increases with molar mass (van der Waals forces), but $H_2O$ has the highest boiling point due to hydrogen bonding. Correct order: $H_2S < H_2Se < H_2Te < H_2O$ So Statement I ($H_2O$ lowest) is incorrect, and Statement II (boiling points of all these hydrides increase with molar mass) is also incorrect because of the anomaly of water. So both statements are incorrect.

Noble gases have only weak dispersion forces between their atoms. So their melting and boiling points are very low, not very high – this statement is incorrect.

H–F (1s–2p), H–Cl (1s–3p), H–Br (1s–4p), H–I (1s–5p) Down the group, the size of the halogen increases, orbital overlap decreases, bond strength decreases, and so the acidic strength increases: HF << HCl << HBr << HI. So both statements are true.

Down group 16, acidic strength increases: $H_2O < H_2S < H_2Se < H_2Te$, so $pK_a$ decreases (not increases). So '$H_2O < H_2S < H_2Se < H_2Te$ : increasing $pK_a$' is not correct. The other sequences are correct.

Peroxodisulphuric acid ($H_2S_2O_8$) contains the peroxo –O–O– linkage:
$HO-SO_2-O-O-SO_2-OH$

On going down the group, the H–E bond dissociation enthalpy decreases, so the thermal stability of $H_2E$ decreases. Order of stability: $H_2Po<H_2Te<H_2Se<H_2S<H_2O$

Tribromooctaoxide is $Br_3O_8$. The three Br atoms are linked in a chain, Br–Br–Br.
Each terminal Br carries three double-bonded O atoms and the central Br carries two double-bonded O atoms, giving 8 O atoms and no formal charges.