MCQ Detailed View

A Lactometer is a scientific instrument used to detect the purity of milk. It works on the principle of density measurement, allowing users to determine whether the milk has been diluted with water or if it meets the natural density of pure milk.

Milk is a liquid that contains water, fats, proteins, sugar (lactose), and minerals. When water is added to milk, its density decreases because water is lighter than milk solids. A lactometer is designed to float in milk and measure its specific gravity, which indicates the relative density of the milk compared to water.

The device is usually made of glass and consists of:

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  A long stem with a graduated scale marked with readings for milk purity.

  
  


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  A weighted bulb that helps the instrument float upright.

  
  

To test milk, the lactometer is gently placed in a container filled with milk. The reading on the scale where the milk level touches the stem tells whether the milk is pure or has been adulterated. Pure cow’s milk typically has a specific gravity of 1.026 to 1.032 at standard temperature. If the reading is lower than this range, it suggests the milk has been watered down.

The other instruments mentioned in the options are used for different purposes:

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  Hygrometer measures humidity (moisture) in the air.

  
  


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  Manometer measures pressure of gases or liquids.

  
  


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  Sonometer is used in physics experiments to study sound vibrations.

  
  

Thus, the correct instrument for detecting milk purity is the Lactometer. This simple tool is widely used in dairy industries, milk shops, and households to ensure the milk being sold or consumed is genuine and free from dilution.