Final answer:
The legal blood alcohol limit in Spain is 250 milligrams per liter (mg/L) of breath, which can be expressed as 250,000 parts per billion (ppb) or micrograms per liter (µg/L).
Step-by-step explanation:
To convert the legal blood alcohol limit in Spain from 250 milligrams per liter (mg/L) of breath to parts per billion (ppb), we need to convert milligrams to micrograms. There are 1000 micrograms in a milligram. Therefore, the blood alcohol limit in Spain can be expressed as 250,000 ppb (250,000 micrograms per liter).