seal and fix cracks in a concrete floor in basement
Is it for cosmetics or is it a matter of sweeping/washing off and things go between the cracks. Finally reason makes a difference. In commercial construction we often use concrete caulk, that way it is the same color and shrinks and expands with weather conditions. Mortar may work but if there is any shifting I would not be surprised if it becomes loose and looks just as bad as before. There are products that help when applying thin layers of concrete/mortar to stick but that it usually for applying an 1/8-1/4 inch. When do that when we are about to stain concrete that was not recently poured.

Note: looking at the pics I would not advise mortar as it would be difficult to fill and stick.

The concrete caulk will fill the gaps and seal it properly. Again the benefit of the caulk is it will shrink and expand if there is minimal shifting, where mortar will not..

Here is a link to for the caulk at home depot. http://www.homedepot.com/p/Red-Devil-10-1-oz-Masonry-and-Concrete-Repair-Caulk-0646/202261765