Everyday Science — Practical Facts

Question 1

Soap works by:‌​‍

Accepted Answer

Emulsifying oil and dirt in water — Soap molecules have a hydrophilic (water-loving) and hydrophobic (oil-loving) end, emulsifying dirt in water.‌​‍

Answer

Killing bacteria

Answer

Bleaching

Answer

Oxidation

Question 2

Why does ice float on water?‌​‍

Accepted Answer

Ice is less dense than water — Water expands when it freezes (anomalous expansion), making ice less dense than liquid water. ‌​‍Maximum density at 4°C.

Answer

Ice is denser

Answer

Ice has more salt

Answer

Ice is colder

Question 3

Pressure cooker cooks faster because:‌​‍

Accepted Answer

Higher boiling point due to increased pressure — Higher pressure raises the boiling point of water above 100°C, cooking food faster.‌​‍

Answer

More heat

Answer

Less water

Answer

Better material

Question 4

Rainbow is caused by:‌​‍

Accepted Answer

Dispersion and total internal reflection of sunlight — Rainbow = sunlight dispersed (split into colours) and internally reflected inside raindrops.‌​‍

Answer

Reflection only

Answer

Refraction only

Answer

Diffraction

Question 5

Why is the sky blue?‌​‍

Accepted Answer

Scattering of blue light by atmosphere — Rayleigh scattering: shorter wavelength blue light is scattered more by atmospheric molecules.‌​‍

Answer

Reflection from ocean

Answer

Blue gases in air

Answer

Ozone layer

Question 6

LPG (cooking gas) mainly contains:‌​‍

Accepted Answer

Butane and Propane — LPG = Liquefied Petroleum Gas, mainly Butane (C₄H₁₀) and Propane (C₃H₈).‌​‍

Answer

Methane

Answer

Hydrogen

Answer

Nitrogen

Question 7

The smell added to LPG for leak detection is:‌​‍

Accepted Answer

Ethyl mercaptan — Ethyl mercaptan (a foul-smelling compound) is added to odourless LPG so leaks can be detected.‌​‍

Answer

Hydrogen sulphide

Answer

Ammonia

Answer

Chlorine

Question 8

Why do we add salt to icy roads?‌​‍

Accepted Answer

Lowers freezing point of water — Salt lowers the freezing point of water (freezing point depression), causing ice to melt.‌​‍

Answer

Makes ice harder

Answer

Makes ice transparent

Answer

Absorbs heat

Question 9

A mirage is seen in deserts due to:‌​‍

Accepted Answer

Total internal reflection of light — Hot air near the ground has lower density → light bends (total internal reflection) → creates illusion of water.‌​‍

Answer

Reflection from sand

Answer

Absorption of light

Answer

Diffraction

Question 10

CFL stands for:‌​‍

Accepted Answer

Compact Fluorescent Lamp — CFL = Compact Fluorescent Lamp. ‌​‍More energy-efficient than incandescent bulbs but being replaced by LEDs.

Answer

Carbon Fluoride Lamp

Answer

Central Fluorescent Light

Answer

Compact Flash Light

Question 11

Hard water does not form lather because it contains:‌​‍

Accepted Answer

Calcium and Magnesium salts — Hard water contains dissolved calcium and magnesium salts that react with soap, preventing lather.‌​‍

Answer

Sodium

Answer

Chlorine

Answer

Iron

Question 12

Rusting requires:‌​‍

Accepted Answer

Both oxygen and water — Rusting = iron + oxygen + moisture → iron oxide (Fe₂O₃). ‌​‍Both O₂ and H₂O are needed.

Answer

Only oxygen

Answer

Only water

Answer

Neither

Question 13

Why does a ball thrown upward come back?‌​‍

Accepted Answer

Gravity — Earth's gravitational force pulls objects toward its centre. ‌​‍The ball decelerates, stops, and falls back.

Answer

Air resistance

Answer

Magnetic force

Answer

Friction

Question 14

The gas used in balloons to make them float is:‌​‍

Accepted Answer

Helium — Helium is lighter than air (second lightest element after hydrogen) and non-flammable, making it safe for balloons.‌​‍

Answer

Oxygen

Answer

Nitrogen

Answer

Carbon Dioxide

Question 15

Why do we feel cool when we sweat?‌​‍

Accepted Answer

Evaporation causes cooling — Evaporation is a cooling process — sweat absorbs body heat when it evaporates, cooling the skin.‌​‍

Answer

Sweat is cold

Answer

Wind blows

Answer

Blood pressure drops

Everyday Science — Practical Facts