Environmental Health

Step 1: Understand the Nalgonda Technique. Step 1: The Nalgonda technique is a water treatment method developed in India to remove excess fluoride. It's a process of chemical precipitation.
Step 2: Arrange the steps of the chemical treatment process.
Step 2:

(A) Addition of two chemicals (lime and alum): First, alum (coagulant) and lime (for alkalinity) are added to the water and mixed rapidly.
(C) Flocculation: The water is then stirred gently. The alum reacts with fluoride and alkalinity to form insoluble aluminum hydroxide flocs that trap the fluoride ions.
(B) Sedimentation: The water is allowed to stand without disturbance. The heavy flocs settle at the bottom of the container.
(D) Filtration: Finally, the clear supernatant water is separated from the sludge, often by filtration, to remove any remaining suspended particles.
Step 3: Conclude the correct sequence.
Step 3: The correct sequence of operations is A C B D.

Step 1: Recall the definition of the Becquerel unit. Step 1: The Becquerel (Bq) is the SI derived unit of radioactivity.
Step 2: Relate the definition to the options.
Step 2: By definition, one Becquerel is the activity of a quantity of radioactive material in which one nucleus decays per second. This directly relates to the activity of a radioactive material.
Step 3: Eliminate other options.
Step 3:

Pathogenic activity relates to disease-causing ability, not measured in Bq.
Chemical activity is measured in terms of reaction rates or concentration (e.g., moles per liter).
Hardness is a physical property measured on scales like Mohs or Vickers.
Therefore, the only correct option is (B).

Step 1: Understand what water hardness is. Step 1: Water hardness is primarily caused by the presence of dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions. It is a measure of the concentration of these mineral salts.
Step 2: Identify the common units for measuring this concentration.
Step 2: The concentration of dissolved substances in water is typically expressed in units that are practical for the low levels found. The most common units for water hardness are:

Milligrams per litre (mg/L).
Parts per million (ppm).
For water, 1 mg/L is equivalent to 1 ppm.
Step 3: Evaluate the options.
Step 3: "Parts per million" is the standard and most frequently used unit among the choices provided. "Parts per trillion" is used for extremely low concentrations (e.g., trace pollutants), while "parts per thousand" and "hundred" are too large for this application.

Step 1: Analyze the WHO definition. Step 1: The definition provided is comprehensive, covering the "control of all factors" in the "physical environment" that can harm human "development, health and survival."
Step 2: Compare the options with this definition.
Step 2:

Environmental Sanitation: This is a subset of environmental health, typically focused on safe disposal of human excreta, water supply, and solid waste. It is not as broad as the given definition.
Environmental Health: This is a broad field that comprises those aspects of human health determined by physical, chemical, biological, social, and psychosocial factors in the environment. The WHO definition given in the question is a classic definition of Environmental Health.
Environmental Standard: This refers to a specific regulation or level that is permissible for a pollutant or environmental factor, not the overall control process.
Environmental Control: This is a general term for actions taken to manage the environment, but "Environmental Health" is the specific public health term defined by the WHO in this context.
Step 3: Conclude the correct term.
Step 3: The definition accurately describes the scope and purpose of Environmental Health.