what are the difference between Merge Rib ends and Merge ends in rib option ?

Merge End is used for Thin Ribs (when profile is open curve and thick option is checked) and Merge Rib's End option trims off extremity of rib to existing material.

Answered with a tutorial: https://grabcad.com/tutorials/what-are-the-difference-between-merge-rib-ends-and-merge-ends-in-rib-option

merge end option is are used for those ribs which are thin(thins the rib profile or slots)
and merge rib's end option is used for trimming those extreme ribs on which material you are working on
follow the links
https://www.youtube.com/watch?v=F84qMhHpzuU
http://www.cadcamengineering.net/trimming-ribs-or-slots-in-catia/

merge end option

merge rib option