Aqueous solution of which salt will not contain ions with the electronic configuration 1s²2s²2p⁶3s²3p⁶ ?

The bond angle H - X - H is the greatest in the compound :

An aqueous solution of a salt MX₂ at certain temperature has a van’t Hoff factor of 2. The degree of dissociation for this solution of the salt is :

If 100 mole of H₂O₂ decompose at 1 bar and 300 K, the work done (kJ) by one mole of O₂(g) as it expands against 1 bar pressure is :

2H₂O₂(l)    $$\rightleftharpoons$$    2H₂O(l) + O₂(g)

(R = 8.3 J K ^$$-$$1 mol^$$-$$1)