Explanation

• The ozone layer is a part of the Earth’s stratosphere that absorbs most of the Sun’s harmful ultraviolet (UV) radiation.
• Without it, UV rays could cause skin cancer, cataracts, and environmental damage.
• It is found approximately 15–35 km above Earth’s surface.

Last verified on 13-03-2026

Explanation

• Conduction is the process of heat transfer through direct contact of molecules.
• In solids, especially metals, molecules vibrate and pass energy to neighboring molecules.
• No movement of the substance itself is required; only energy is transferred.

Last verified on 13-03-2026

Explanation

• A thermal conductor is a material that allows heat to pass through it easily.
• Metals like copper, aluminum, and iron are good thermal conductors.
• Thermal conduction occurs mainly in solids where particles are closely packed.
• In contrast, thermal insulators (like wood, plastic, and rubber) resist heat flow.

Last verified on 13-03-2026

Explanation

• Green plants use carbon dioxide (CO₂) from the atmosphere to make food via photosynthesis.
• In photosynthesis, CO₂ + H₂O → Glucose + O₂ (with sunlight and chlorophyll).

Last verified on 13-03-2026

Explanation

• The symbol ⁴₂He indicates helium has 2 protons (atomic number = 2) and mass number = 4.
• In a neutral atom, the number of electrons = protons, so helium has 2 electrons.

Last verified on 13-03-2026

Explanation

• The same atomic number (Z) → same number of protons
• Different mass numbers → different number of neutrons

Explanation

• Sublimation is the direct transition of a solid into a gas without passing through the liquid phase.

Additional information:

Some common sublimating substances:

• Dry ice (CO₂) – solid → gas
• Iodine crystals – solid → violet gas
• Camphor – solid → vapor
• Naphthalene (mothballs) – solid → gas
• Ammonium chloride – solid → gas

Last verified on 13-03-2026

Explanation

• The freezing point of water is 0°C (32°F), where water changes from liquid to solid.
• The melting point is also 0°C, where ice changes from solid to liquid.
• Freezing and melting are opposite processes occurring at the same temperature.

Last verified on 13-03-2026

Explanation

• Liquids have no fixed shape but have a fixed volume.
• Particles are close together but can slide past each other, allowing the liquid to flow.

Additional information:

• Solid: Are tightly packed and stay in a fixed position
• Gas: Are widely spaced and move freely in any direction

Last verified on 13-03-2026

Explanation

• Glucose is a simple sugar (monosaccharide) and a primary source of energy for cells.
• Its chemical formula is C6H12O6.

Additional information:

• Fructose: C6H12O6 (same formula as glucose, different structure)
• Galactose: C6H12O6
• Ribose: C5H10O5
• Deoxyribose: C5H10O4
• Sucrose (disaccharide): C12H22O11

Last verified on 13-03-2026