Explanation

• The density of gases increases when pressure is increased because gas molecules come closer together.
• Density is the mass per unit volume of a substance.
• When pressure increases, the volume of gas decreases (at constant temperature), causing density to increase.
• This relationship follows Boyle’s Law.

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

• Alcohol is soluble in water (can dissolve in water).
• It forms hydrogen bonds with water molecules.
• Common example: ethanol mixes completely with water.

Last verified on 20-06-2026

Explanation

• Between the melting point and boiling point, a substance exists in the liquid state.
• At melting point, solid changes into liquid.
• At boiling point, liquid changes into gas.
• So in between these two points, the substance remains stable as a liquid.

Last verified on 20-06-2026