Certified Instrument Specialist (CIS) 2025 Practice Exam – 400 Free Practice Questions to Pass the Exam

Deionized water (DI) refers specifically to water that has been purified by removing charged ions, primarily minerals such as calcium, magnesium, sodium, and chloride. This process typically involves ion exchange or membrane filtration methods that target and eliminate these impurities, which can interfere with chemical reactions and analytical procedures. The result is water that is largely free from dissolved salts and is often used in laboratory settings, industrial applications, and various scientific processes where high purity is essential.

The other options highlight aspects related to different types of water treatment or purification but do not accurately describe the essence of deionized water. For instance, while some treatments might involve removing bacteria or contaminants, these processes do not necessarily relate to the removal of ions, which is the core characteristic defining deionized water. Thus, the key understanding here is that deionized water emphasizes the absence of dissolved ionic species, which is crucial for many precision applications.