118) When a white hygroscopic powder X is treated with cold water, a compound Y is formed, which forms a white precipitate with BaCl₂ in acidic medium. Y also gives a white amorphous precipitate with neutral AgNO₃. Compound Y can also be obtained by heating H₃PO₄. X and Y are:

119) A compound A of S, Cl and O has a vapour density of 67.5. It reacts with water to form two acids and reacts with KOH to form two salts B and C. B gives white precipitate with AgNO₃ solution and C gives white precipitate with BaCl₂ solution. Identify A.

120) When Cl₂ is passed through hot conc. NaOH, salts A and B are formed, which are separated by fractional crystallization. When B is treated with a calculated amount of KCl, a substance C is produced. When C is gently heated, it disproportionates to give D and E. When E is heated with conc. H₂SO₄, the strongest Bronsted acid F is formed, which is isoelectronic with H₂SO₄. Identify F.

121) PCl₃ and PCl₅ both exist; NCl₃ exists, but NCl₅ does not. This is due to:

122) Number of lone pair of electrons on Xe atoms in XeF₂, XeF₄ and XeF₆ molecules are respectively: