Everyday Science

The ionosphere contains charged particles that reflect radio waves back to Earth, enabling long-distance radio communication. Other layers like the exosphere, troposphere, and stratosphere do not have this property.

The primary stimulant found in tea leaves is caffeine, which is responsible for the stimulating effects of tea. Theine is an older term for caffeine but is chemically the same compound, so caffeine is the most accurate and widely accepted term.

Steam can penetrate the skin more effectively than boiling water because it condenses on the skin, releasing latent heat and causing deeper burns. This makes scalding with steam more severe than with boiling water, even though both are at similar temperatures.

An oasis is a fertile spot in a desert where water is found, allowing vegetation to grow. Therefore, it is directly associated with deserts.

The sun appears red at sunrise and sunset because the sunlight passes through a thicker layer of the atmosphere, causing shorter wavelengths (blue and green) to scatter out and leaving the longer red wavelengths to reach the observer. This scattering is due to dust particles and air molecules in the atmosphere.

ECG (Electrocardiogram) is a diagnostic tool used to measure the electrical activity of the heart, helping to identify heart-related ailments.

Cow's milk typically contains about 87% to 88% water by weight. Among the given options, 80% is the closest to the actual water content of cow's milk. The other options (60%, 65%, and 72%) are significantly lower than the true value. Therefore, the correct answer is 80%.

Most asteroids are located in the asteroid belt, which lies between the orbits of Mars and Jupiter. This region contains numerous rocky bodies orbiting the Sun, making option A correct.

Diesel engines do not use spark plugs because they ignite the fuel-air mixture through compression, not a spark. Therefore, the number of spark plugs needed in a diesel engine is zero.

The main component of bones and teeth is calcium phosphate, primarily in the form of hydroxyapatite, which provides strength and rigidity. Other calcium compounds like calcium carbonate, sulphate, or nitrate are not the primary constituents of bones and teeth.