The oxoacid of phosphorus that is easily obtained from a reaction of alkali and white phosphorus and has two P-H bonds, is :

The acid that is believed to be mainly responsible for the damage of Taj Mahal is :

Two isomers 'A' and 'B' with molecular formula C₄H₈ give different products on oxidation with KMnO₄ in acidic medium. Isomer 'A' on reaction with KMnO₄/H⁺ results in effervescence of a gas and gives ketone. The compound 'A' is

In the given conversion the compound A is :