Information:  - The micrometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: m) or micrometer (American spelling), also commonly known as a micron, is an SI derived unit of length equaling 1×10 of a metre (SI standard prefix "micro-" = 10); that is, one millionth of a metre (or one thousandth of a millimetre, 0.001 mm, or about 0.000039 inch). The symbol m is sometimes rendered as um if the symbol  cannot be used, or if the writer is not aware of the distinction.  - Radioactive waste is waste that contains radioactive material. Radioactive waste is usually a by-product of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine. Radioactive waste is hazardous to most forms of life and the environment, and is regulated by government agencies in order to protect human health and the environment.  - A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant, or other type of organism. The term typically refers to the zone in which the organism lives and where it can find food, shelter, protection and mates for reproduction. It is the natural environment in which an organism lives, or the physical environment that surrounds a species population.  - Disinfectants are antimicrobial agents that are applied to non-living objects to destroy microorganisms that are living on the objects . Disinfection does not necessarily kill all microorganisms , especially resistant bacterial spores ; it is less effective than sterilization , which is an extreme physical and / or chemical process that kills all types of life . Disinfectants are different from other antimicrobial agents such as antibiotics , which destroy microorganisms within the body , and antiseptics , which destroy microorganisms on living tissue . Disinfectants are also different from biocides -- the latter are intended to destroy all forms of life , not just microorganisms . Disinfectants work by destroying the cell wall of microbes or interfering with the metabolism . Sanitizers are substances that simultaneously clean and disinfect . Disinfectants are frequently used in hospitals , dental surgeries , kitchens , and bathrooms to kill infectious organisms . Bacterial endospores are most resistant to disinfectants , but some viruses and bacteria also possess some tolerance . In wastewater treatment , a disinfection step with chlorine , ultra-violet ( UV ) radiation or ozonation can be included as tertiary treatment to remove pathogens from wastewater , for example if it is to be reused to irrigate golf courses . An alternative term used in the sanitation sector for disinfection of waste streams , sewage sludge or fecal sludge is sanitisation or sanitization .  - An ion is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by either chemical or physical means, via ionization.  - Earth, otherwise known as the world, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets.  - A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means. The US Environmental Protection Agency (EPA) uses a slightly different definition for biocides as "a diverse group of poisonous substances including preservatives, insecticides, disinfectants, and pesticides used for the control of organisms that are harmful to human or animal health or that cause damage to natural or manufactured products". When compared, the two definitions roughly imply the same, although the US EPA definition includes plant protection products and some veterinary medicines.  - Bacteria (common noun bacteria, singular bacterium) constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals.    After reading the paragraphs above, we are interested in knowing the entity with which 'disinfectant' exhibits the relationship of 'subclass of'. Find the answer from the choices below.  Choices: - animal  - area  - atom  - bacteria  - charge  - chemical substance  - habitat  - ion  - length  - life  - material  - medicine  - metre  - natural  - natural environment  - noun  - number  - object  - planet  - plant  - population  - power  - research  - species  - symbol  - technology  - term  - via  - water  - world  - writer
The answer to this question is:
chemical substance