Explanation

• Reaction rate depends on collision frequency and energy.
• Temperature, pressure, and surface area increase collision number.
• A catalyst increases reaction rate but does not change collisions directly.
• It works by lowering activation energy, not by changing collisions.

Last verified on 11-04-2026

Explanation

• H₂O(g) → 2H(g) + O₂(g)
• Endothermic reactions absorb heat from the surroundings.
• Breaking bonds requires energy input.
• Water vapour (H₂O) is broken into atoms, which needs energy.
• Therefore, this process is endothermic.

Last verified on 11-04-2026

Explanation

• Some ions release gas in specific chemical reactions.
• Ammonium ions release ammonia gas when reacting with alkali.
• Carbonate ions release carbon dioxide gas when reacting with acid.
• Since gas is produced with both acid and alkali, both ions must be present.

Last verified on 11-04-2026

Explanation

• A redox reaction involves oxidation and reduction together.
• Oxidation = loss of electrons, Reduction = gain of electrons.
• The substance that loses electrons is called the reducing agent.
• Therefore, electrons are transferred from the reducing agent to another substance.

Last verified on 11-04-2026

Explanation

• Soap is made by a chemical reaction of fats or oils with alkali.
• This industrial process is called saponification.
• It produces soap and glycerol as products.

Last verified on 11-04-2026

Explanation

Mr of MgCO₃ = 84  

Mr of MgO = 24 + 16 = 40  

Moles of MgCO₃ = 21.0 g ÷ 84 g/mol = 0.25 mol  

From equation: 1 mol MgCO₃ → 1 mol MgO  

So 0.25 mol MgCO₃ → 0.25 mol MgO  

Mass of MgO = 0.25 mol × 40 g/mol = 10.0 g

Last verified on 11-04-2026

Explanation

• Changes of state involve transformation between solid, liquid, and gas.
• Sublimation is a direct change from solid to gas.
• In this process, particles move from a fixed arrangement to widely spaced.
• No liquid phase is involved in between.
• This change is called sublimation.
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Last verified on 11-04-2026

Explanation

• X-rays are a form of electromagnetic radiation.
• They are produced in X-ray tubes.
• High-speed cathode rays (electrons) hit a solid target.
• The sudden stopping of electrons produces X-rays.
• The target is usually made of metal (like tungsten).

Last verified on 11-04-2026

Explanation

• In aquatic ecosystems, algae are primary producers.
• They form the base of the food chain in ponds.
• Fish indirectly depend on algae for food (via food chain).
• Removing algae disrupts energy flow in the ecosystem.
• This reduces fish population due to lack of food support.

Last verified on 10-04-2026

Explanation

• Evolution explains how organisms change over time.
• Homologous structures have similar origin but different functions.
• They are found in different species with a common ancestor.
• Their structure indicates evolutionary relationships.
• Therefore, they support the idea of common ancestry.

Last verified on 10-04-2026