Final answer:
In the play A Doll's House, Nora gives a bond to Serafina to send by post to her father, Krogstad. This act triggers the events that unfold the secrets and lies within her marriage.
Step-by-step explanation:
In the play A Doll's House by Henrik Ibsen, Nora gives a bond to Serafina to send by post to her father, Krogstad. The bond is an important plot element that drives the conflict in the play. Nora's act of giving the bond to Serafina unknowingly sets off a series of events that reveal the secrets and lies within her marriage and ultimately lead to her liberation.