reactions of ethers

In the reaction of ethers , the fission of the following bond takes place :

Reaction of ether with HI is preferred than HBr because _________.

Assertion: Methoxy ethane reacts with HI to give ethanol and iodomethane Reason: Reaction of ether with HI follows S_(N)^(2) mechanism

In which of the following reactions ether does not form ?

Compounds (A) and (B) on reaction in ether medium and subsequent acidification and oxidation give 2,5-dimetylhexan-3-one. What are (A) and (B) ?