Which of the following inorganic substances can be found in water?

The chosen answer identifies arsenic, lead, mercury, and nitrate as inorganic substances that can be found in water. Each of these substances is relevant in the context of water quality and public health.

Arsenic is a naturally occurring element that can leach into groundwater from certain rocks and minerals. It poses significant health risks, including cancer and skin lesions. Lead is commonly associated with aging plumbing systems and can contaminate drinking water, leading to serious health issues, particularly in children. Mercury is another toxic metal that can enter water systems through industrial discharge and mining activities, affecting aquatic ecosystems and human health. Nitrate, primarily from agricultural runoff and fertilizers, can result in health problems such as methemoglobinemia, or "blue baby syndrome," and can lead to eutrophication of water bodies.

While calcium and magnesium, sodium and potassium, as well as chlorine and fluoride, are also inorganic substances found in water, the presence of arsenic, lead, and mercury highlights primary concerns related to contamination and toxicity. This distinction makes option B particularly significant when discussing the potential hazards that certain inorganic substances can pose to water quality and public health standards.