Which branched chain isomer of the hydrocarbon with molecular mass 72u gives only one isomer of mono substituted alkyl halide?

Arrange the following compounds in order of decreasing acidity :

Compound (A), C₈H₉Br, gives a white precipitate when warmed with alcoholic AgNO₃. Oxidation of (A) gives an acid (B), C₈H₆O₄. (B) easily forms anhydride on heating. Identify the compound (A).

An organic compound A upon reacting with NH₃ gives B. On heating B give C, C in presence of KOH reacts with Br₂ to give CH₃CH₂NH₂. A is :

The total number of basic groups in the following form of lysine is