How does the interaction between helmer and nora advance the plot?

helmer decides he might need to use strength against krogstad to make him leave his position at the bank.
helmer realizes that nora is right about krogstad, which will keep her secret safe from him later in the play.
helmer thinks that nora is afraid his reputation will suffer, heightening the suspense about her real secret.
helmer agrees with nora that it is too late and that he has made a mistake with krogstad, which creates conflict.