Which of the following best explains why Lignocaine has a higher fetal-to-maternal plasma ratio when compared with bupivacaine?
Bupivacaine has low molecular weight
Lignocaine has higher protein-binding
Bupivacaine has a lower dissociation constant (pKa)
Lignocaine is less protein bound
Lignocaine is  less protein bound than bupivacaine. Unbound form of drug thus easily gets transferred across placenta.