The correct decreasing order of acidity for the most acidic hydrogen atom in the following compounds is: (I) 1,3-cyclopentadiene (II) 1-butyne (III) 1-butene (IV) butane

Step-by-step solution

Acidity is directly proportional to the stability of the conjugate base formed after the removal of a proton ( H^+ ). For (I) 1,3-cyclopentadiene, the removal of a proton from the sp^3 hybridized carbon yields the cyclopentadienyl anion. This anion is planar, cyclic, completely conjugated, and has 6 electrons, making it aromatic and exceptionally stable. For (II) 1-butyne, the terminal hydrogen is attached to an sp hybridized carbon (50 % s-character), making the resulting carbanion relatively stable due to the hig