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

• 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

• An Addition Reaction is a chemical reaction in which two or more substances combine to form a single compound.
• It is also called a Combination Reaction in basic chemistry.
• This reaction usually releases heat or energy.

Last verified on 12-03-2026

Explanation

• A chemical reaction that releases heat energy to the surroundings is called an Exothermic Reaction.
• In such reactions, energy is produced in the form of heat, light, or flames.
• Examples include combustion of fuel, respiration, and neutralization reactions.

Additional information:

• An endothermic reaction, which absorbs heat from the surroundings.

Last verified on 11-03-2026

Explanation

• The branch of chemistry that studies heat energy released or absorbed during chemical reactions is called Thermochemistry.
• It explains how heat changes occur during reactions such as combustion, neutralization, and dissolution.
• It deals with concepts like enthalpy change (ΔH), exothermic reactions, and endothermic reactions.

Last verified on 11-03-2026

Explanation

• The formation of hydrogen and oxygen from water, which is an example of a decomposition reaction: 2H2O → 2H2 + O2
• In this reaction, water (H2O) decomposes into hydrogen (H2) and oxygen (O2).

Last verified on 11-03-2026

Explanation

• Antoine Lavoisier, a French chemist, is credited with discovering the law of conservation of mass in 1789 (1785).
• He demonstrated that matter cannot be created or destroyed in a chemical reaction, only transformed from one substance to another.

Last verified on 10-03-2026