Explanation

• An echo is a sound that reflects off a surface and is heard again.
• It occurs when sound waves bounce back from a distant surface like a wall or mountain.
• Echoes are common in caves, valleys, and empty halls.
• The reflected sound is perceived after a short delay.

Last verified on 17-03-2026

Explanation

• Total internal reflection occurs when light travels from a denser medium to a rarer medium.
• The angle of incidence must be greater than the critical angle for the two media.
• Light is completely reflected back into the denser medium instead of refracting.
• Common examples: optical fibers, diamonds, and mirages.

Last verified on 17-03-2026

Explanation

• Ions are charged particles formed when an atom gains or loses electrons.
• Loss of electrons creates a positively charged ion (cation).
• Gain of electrons creates a negatively charged ion (anion).

Last verified on 17-03-2026

Explanation

• A change in physical appearance or state of a substance, such as a change in shape, size, color, or phase (solid, liquid, gas), is called a Physical Change.
  

The are examples of Physical Changes:

• Melting (ice cream, wax, chocolate, ice and change from solid to liquid)
• Phase changes (boiling, freezing, condensation)
• Crushing (chalk)
• Tearing (paper)
• Crumpling (aluminium foil)
• Stretching (rubber band)
• Mixing (sugar in water)
• Dissolving (sugar, salt in water)
• Moulding (clay, metals)
• Slicing (fruit)
• Forming of frost (from water vapors)
• Transition to a gas (change from liquid to gas)
• Change of durability (change in texture or strength)
• Changes to crystal form (change in crystal structure)

Last verified on 17-03-2026

Explanation

• A mature, large ovary and seed are characteristics of a fruit.
• A fruit is the mature ovary of a plant, which contains seeds.
• It typically surrounded by a fleshy, edible pulp.

Last verified on 17-03-2026

Explanation

• Root hairs are tiny tubular outgrowths of roots in plants.
• They increase the surface area of roots for efficient absorption.
• Their main function is to absorb water, mineral salts, and gases from the soil.
• They do not perform photosynthesis or reproduction.

Last verified on 17-03-2026

Explanation

• Air is essential for plants because they need gases from the air for survival and growth.
• Plants take carbon dioxide (CO₂) from the air during photosynthesis to make their food.
• They also use oxygen (O₂) from the air for respiration to release energy.
• Without air, plants cannot perform important life processes.

Last verified on 16-03-2026

Explanation

• Dilution refers to the process of decreasing the concentration of a solution by adding more solvent.
• While ionisation involves the formation of ions from molecules in a solution.

Last verified on 16-03-2026

Explanation

• Citric acid is a natural preservative found in many fruits, particularly in citrus fruits like lemons, oranges, and grapefruits.
• It's responsible for their sour taste and is also used as a food additive.
• Other fruits like mangoes, grapes, and strawberries also contain citric acid, although in smaller amounts.
• The presence of citric acid gives these fruits their characteristic sour taste.

Last verified on 16-03-2026

Explanation

• When light is focused in front of the retina, it creates a blurred image, indicating nearsightedness (myopia).
• This occurs because the eyeball is too long or the cornea is too steep.
• It causing light to focus before reaching the retina.

Last verified on 16-03-2026