801. The half-life of a radioactive element is 8 days. It takes 8 days to reduce it from 10 mg to 5 mg.
802. The phenomenon of Aurora Borealis, the display of red and green lights in the northern hemisphere, is due to radiations from the ionosphere.
803. The echo will be distinctly heard only at ordinary temperatures if the distance of the reflecting surfaces from the source of sound is at least 56 ft.
804. A lactometer is used to measure the specific gravity of milk.
805. In humans, most nutrient molecules are absorbed by the small intestine.
806. The main constituent of hemoglobin is iron.
807. Vitamin A promotes healthy functioning of eyes in human beings.
808. ECG is used for the diagnosis of ailments of the heart.
809. An astronaut inside a spacecraft is in a state of weightlessness, implying that the astronaut and the spacecraft are both in a free-falling state.
810. Lead ball falls through water more slowly than through air due to the viscous force in water.
811. Materials for rain-proof coats and tents owe their waterproof properties to surface tension.
812. Sunlight can reach a depth of 200 meters in the ocean.
813. Equator passes through none of these countries.
814. Beta particles are fast-moving electrons.
815. It is impossible for a type O+ baby to have a type AB- mother.
816. The main culprit in the thinning of the ozone layer in the Earth’s stratosphere is chlorofluorocarbons (CFCs).
817. Matter is anything that takes up space and has mass.
818. The speed of light is 300,000 km/s.
819. The energy stored in a dam is potential energy.
820. The distance of Mercury from the Sun is 57.9 million km.

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