In ealier versions I could right-click on the object and then select merge with background, I no longer have this option, where did it go?
Usually the option is not available because the slide is using a Master Slide. Clear the Master Slide option and you should see the option re-appear on the menu.
Helpful and Handy Links
Check the Properties panel, if this slide has 'Use Master Slide Background' checked in the General accordion, then the Merge will not be available because you have to merge this object in the Master slide with its background. Hope this makes sense?