Explanation

• Rutherford’s gold foil experiment (1911) showed that an atom has a small, dense, positively charged center called the nucleus.
• The mass of the atom is concentrated in the nucleus, while most of the atom is empty space.

Additional information:

• Nucleus contains: Protons (+) and neutrons (neutral)
• Electrons move around the nucleus in mostly empty space
• The experiment involved alpha particles being deflected by the nucleus.

Last verified on 10-02-2026

Explanation

• Organic compounds (like hydrocarbons, sugars, fats) are highly combustible.
• This is due to their high carbon content, which releases energy when burned.
• Carbon forms stable bonds that release heat and energy during combustion.

Last verified on 10-02-2026

Explanation

• The ozone layer absorbs and blocks the majority of the Sun’s harmful ultraviolet (UV) radiation.
• This protection helps prevent skin cancer, cataracts, and damage to ecosystems.

Last verified on 09-02-2026

Explanation

• Endothermic reactions absorb heat from the surroundings (e.g., photosynthesis, melting ice).
• Exothermic reactions release heat to the surroundings (e.g., burning fuel, respiration).
• The key difference is heat flow direction between the system and environment.

Additional information:

• Endothermic → feels cold to touch
• Exothermic → feels hot to touch
• Examples help remember: Ice melting (endo), Fire burning (exo)

Last verified on 09-02-2026

Explanation

• Endothermic reactions absorb heat from the surroundings.

Examples:

• Photosynthesis → plants absorb sunlight to make glucose
• Melting of ice → absorbs heat to change solid → liquid
• Dissolving ammonium nitrate in water → absorbs heat, feels cold

Burning of fuel is exothermic, releasing heat and light.

Last verified on 09-02-2026