Which of the following  is least mineralized?
The physical occlusion of the tubular lumens increases the ability of light to pass through this localized region (i.e., increases its transparency). This dentin is referred to as transparent dentin. Dentin in this area is not as hard as normal primary dentin because of mineral loss in the intertubular dentin.
Successful host-defense repair processes result in the remineralization of the intertubular dentin, in addition to the mineral occlusion of the dentinal tubules, such that the final hardness of the dentin in this affected area is greater than normal primary dentin.
The increased overall mineralization of this caries-affected primary dentin is referred to as reactive dentin sclerosis.
Deep dentin formation processes occur simultaneously with the pulpal inflammatory response and result in the generation of tertiary dentin at the pulp–dentin interface. Two types of tertiary dentin form in response to lesion formation. 

Reference: Sturdevant operative dentistry. 7th edition Page no 10
Transparent dentin
Reactive dentin sclerosis
Reparative dentin
Reactionary dentin