Identify A in the following reaction.

In the following sequence of reactions a compound A, (molecular formula C₆H₁₂O₂) with a straight chain structure gives a C₄ carboxylic acid. A is :

The Crystal Field Stabilization Energy (CFSE) and magnetic moment (spin-only) of an octahedral aqua complex of a metal ion (M^z+) are $$-$$0.8 $$\Delta$$₀ and 3.87 BM, respectively. Identify (M^z+) :

Which one of the following compounds is aromatic in nature?