Everyday Science

A human can typically survive without food for about one month, depending on factors like hydration and health. Survival beyond this period without food is rare and generally not sustainable.

Copper is one of the few metals that commonly occurs in a free (native) state in nature, unlike lead, iron, or mercury which are usually found in combined forms (ores).

Eratosthenes was the first known person to calculate the Earth's radius (and circumference) accurately by measuring the angle of the sun's rays at two different locations and using geometry.

Nicotine is the primary addictive substance found in tobacco, responsible for the dependence associated with tobacco use. Ethanol is alcohol, ammonia is a chemical sometimes found in tobacco smoke but not addictive, and tar is a harmful residue but not addictive.

Proxima Centauri is the closest known star to our Sun, located about 4.24 light-years away in the Alpha Centauri star system. The other options are much farther away.

Spring tides occur during new moon and full moon phases because the gravitational forces of the sun and moon align, pulling the ocean's water in the same direction, which happens when the sun, moon, and earth are in a straight line.

The Big Bang is estimated by cosmologists to have occurred approximately 13.8 billion years ago, which is closest to option B (15 billion years ago) among the given choices. This event marks the origin of the universe.

Vitamin A is primarily found in yellow and orange vegetables, such as carrots and pumpkins, which contain beta-carotene that the body converts into vitamin A. Green vegetables also contain some vitamin A, but yellow vegetables are more characteristic sources.

Water vapor is the gaseous form of water, invisible and present in the air. It is not a cloud droplet, raindrop, or snowflake, which are all forms of liquid or solid water.

The boiling point of water primarily depends on air pressure; at higher altitudes where air pressure is lower, water boils at lower temperatures. Air temperature, relative humidity, and air density have negligible direct effects on the boiling point.