If you are on old mobile you can craft 3 shocking tranq darts at a time using bio toxin, 2 metal ingots, and 1 tranq dart. If you are on other versions you can only craft 1 at a time using the same amount of ingredients.

Also for some reason at least on old mobile they count as "tranq darts" to make more tranq darts, so you don't actually need a regular tranq dart to craft more shocking tranq darts as shocking tranq darts will work.