Soaps clean surfaces on the principle based on
- A.Viscosity
- B.Floatation
- C.Elasticity
- D.Surface tension
Correct answer
Explanation
The correct answer is D, Surface tension. Soap lowers the surface tension of water, so water spreads into fine gaps and wets greasy dirt that plain water would bead up on.
A soap molecule is a long chain with an ionic head that attracts water and a hydrocarbon tail that attracts oil. Gathering at the surface, these molecules reduce the surface tension of water and make it a better wetting agent. In the wash, the tails dig into grease while the heads stay in water, and the molecules form clusters called micelles with the oily dirt trapped inside. Rinsing then carries the micelles away. Detergents work on the same principle and also lather in hard water.
A is wrong because viscosity, the internal friction of a fluid, plays no part in cleaning.
B is wrong because floatation is a method of concentrating ores by froth, not the reason soap cleans.
C is wrong because elasticity concerns solids regaining shape after a force is removed.
Exam tip: soap lowers surface tension and forms micelles; hydrophilic head, hydrophobic tail.
Practice Questions
View allWhich one of the following can charge an insulator?
- A.Current electricity
- B.Static electricity
- C.Magnetic field
- D.Gravitational field
Show answer
An insulator is charged by friction: rubbing transfers electrons from one surface to another, and because electrons cannot move through an insulator, the charge stays where it is as static electricity.
Read the full explanation →A glass prism splits white light into different colours. This phenomenon is called dispersion of light by prism. Which one of the following statements is correct?
- A.Red light will deviate the most and it is because of the reflection of light.
- B.Violet light will deviate the most and it is because of the refraction of light.
- C.Red light will deviate the most and it is because of the refraction of light.
- D.Violet light will deviate the most and it is because of the reflection of light.
Show answer
In glass, violet light has the shortest wavelength and the highest refractive index, so it bends the most; dispersion is a result of refraction.
Read the full explanation →A 5 N force is defined when a mass of 10 kg is accelerated with
- A.5.0 cm/s²
- B.0.5 m/s²
- C.0.5 cm/s²
- D.5.0 m/s²
Show answer
By Newton's second law, F = m × a, so a = F ÷ m = 5 N ÷ 10 kg = 0.5 m/s².
Read the full explanation →The breakdown of glucose in cytoplasm results in the formation of
- A.pyruvate and energy
- B.pyruvate and carbon dioxide
- C.pyruvate and oxygen
- D.pyruvate and nitrogen
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In the cytoplasm, glucose is split by glycolysis into two molecules of pyruvate, releasing a small amount of energy as ATP.
Read the full explanation →Which one of the following is the correct sequence in increasing complexity?
- A.Protein - Organism - Tissue - Organ
- B.Protein - Organ - Tissue - Organism
- C.Protein - Organism - Organ - Tissue
- D.Protein - Tissue - Organ - Organism
Show answer
Living things are built up level by level: molecules such as proteins form cells, cells form tissues, tissues form organs, organs form organ systems, and these together make an organism.
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