As per Steve Zipay, the Rangers will extend a qualifying offer to RFA Brandon Prust. Prust, who made $500,000 last season, would receive an offer of approximately $550,000-$600,000 for a one year deal. By extending a QO, the Rangers ensure that they will receive compensation if Prust signs an offer sheet. Compensation will vary based on amount of the deal (details here).
Meanwhile, the Rangers will not extend a QO to RFA Erik Christensen. Christensen, who made $850,000 last season, would receive a QO of approximately $900,000, probably a bit more, for one year. In doing so, the Rangers hope to sign Christensen to a deal for more years, and less money. It is risky, but considering that Christensen was claimed off waivers, it was unlikely he would receive a big offer from another team.