O is what should go in the blank. O stands for Oxygen.
Answer:
NaOH
Explanation:
Look at charge Na has +1 charge and Ca has +2 charge after dissociation . Greater charge Stronger lattice. And as we need weak Lattice, so NaoH is stronger base than Ca(OH)2.
I think Geothermal but I’m not 100% sure
Tarnish is Ag2S-silver sulfide and the oxidation state of silver is +1
Answer:
(c) 
Explanation:
The solubility product of a solid is the amount of solid dissociates into its respective ions in the solution. Thus more the value of the Ksp, the more is the salt soluble in the solvent.
So, Given that:-




The salt having highest value of Ksp is AgCN. So, it is most soluble.