Average bond strength of second generation dentin bonding agents:: (A) 2-5 MPA, (B) 12-18 MPA, (C) 20-23 MPA, (D) 25-30 MPA
Answer is A. SECOND GEN - Contains halophosphorus esters of unfilled resins.
Mechanism of bonding Is by ionic bond to calcium by chlorophosphate groups.
Eg: scotchbond, bondlite. 
Disadvantages: 

Again poor bond strength 2-5 MPA. 
Hydrolysis of bond. 
Bonds to smear layer.  

Reference-Sturdevant 6th ed  Pg: 116