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:

123) Which one of the following substances has the highest proton affinity?

124) What is expected to happen when phosphine gas is mixed with chlorine gas?