The one on the right was left on the vine too long.
Cukes are picked while still green. So, with the yellowing, you now have a ripe cucumber. Still edible. You can search for possible uses/recipes.

Once the vine begins to produce cukes, harvest every day or two. If cukes are allowed to ripen, the vine will shut down further production.

The cuke on the left wasn't completely pollinated and is also "ripe."