Explanation

• The audible range of a normal human ear is 20 Hz to 20,000 Hz (20 kHz).
• Sounds below this range are called infrasound,
• Sounds above it are called ultrasound. 
• Lower limit: 20 Hz (deep rumbles)
• Upper limit: 20,000 Hz (high-pitched squeaks)

Additional information

• Adult change: The upper limit often drops to 15,000–17,000 Hz as people get older. 
• Unit of frequency: Hertz (Hz)

Last updated 27-07-2026 by NA

Explanation

• The mass of a proton is approximately 1836 times greater than the mass of an electron.
• A proton is a positively charged particle found in the nucleus of an atom.
• It has almost the same mass as a neutron (slightly less).
• Electrons are much lighter compared to protons.

Last verified on 22-06-2026

Explanation

• Theory proposed by: Charles Darwin
• Book published: 1859
• Book name: On the Origin of Species
• Key concept: Natural Selection
• Voyage that inspired him: HMS Beagle expedition (1831–1836)

Last verified on 21-06-2026

Explanation

• Lead pencil is made up of graphite.
• Graphite is a form (allotrope) of carbon.
• It is soft and leaves marks on paper easily.
• It is used in pencils because of its slippery layered structure.
• Despite the name “lead pencil,” it contains no real lead.
• Graphite was named by Abraham Gottlob Werner in 1789.

Last verified on 21-06-2026

Explanation

• Diamond is a naturally occurring allotropic form of carbon.
• Allotropy means a single element can exist in more than one form with different structures and properties.
• It is extremely hard.
• It has a high melting point.
• It is widely used in jewelry and cutting tools.

Additional information:

• Graphite – soft, good conductor
• Fullerenes (C60) – spherical molecules
• Carbon nanotubes – tubular, high strength
• Amorphous carbon – coal, soot
• Lonsdaleite – hexagonal diamond

Last verified on 17-01-2026

Explanation

• Total standard zones: 24
• Earth rotation time: 24 hours
• Longitude per zone: 15 degrees
• Starting point: Greenwich (0°)
• It is used worldwide for time coordination.

Last verified on 14-06-2026

Explanation

• Chromosomes are made of DNA and proteins.
• DNA carries genetic information.
• Proteins (mainly histones) help package DNA.
• Together they form chromatin material.
• Chromosomes are found in the nucleus of cells.

Last verified on 18-06-2026

Explanation

• Solvent extraction is controlled by the Distribution Law (Nernst Distribution Law).
• It describes how a solute distributes between two immiscible liquids.
• At equilibrium, the concentration ratio remains constant.
• This law governs equilibrium in extraction processes.

Last verified on 18-06-2026

Explanation

• Calcium chloride (CaCl₂) is used as a drying agent in a desiccator.
• It absorbs moisture from the air.
• It keeps substances dry and free from water vapor.
• Desiccators are used in laboratories for drying chemicals.
• CaCl₂ is highly hygroscopic.

Last verified 18-06-2026

Explanation

• Chile saltpeter is the common name for sodium nitrate (NaNO₃).
• It is found naturally in Chile and Peru.
• It is used in fertilizers and explosives.

Last verified on 18-06-2026