Basic Science

Explanation: Mercury orbits only 58 million km from the Sun. A Mercurian year lasts just 88 Earth days. It is also the smallest planet. Despite its proximity to the Sun, it is not the hottest: Venus, with its greenhouse effect, holds that record.

Explanation: Since 2006, the solar system has 8 planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was reclassified as a "dwarf planet" by the International Astronomical Union.

Explanation: Sodium chloride (NaCl) is composed of one sodium atom (Na) and one chlorine atom (Cl). Salt was so precious in ancient times that Roman soldiers were sometimes paid in salt, hence the word "salary" (from Latin salarium).

Explanation: Gravity is the force of attraction that the Earth exerts on objects. Isaac Newton formalized it in 1687 after observing a falling apple.

Explanation: H2O means 2 hydrogen atoms and 1 oxygen atom.

Explanation: Humans have 23 pairs of chromosomes, or 46 in total. Gametes (sperm and eggs) only have 23.

Explanation: The skin weighs about 4 kg and covers 2 m² in an adult.

Explanation: Light travels at about 300,000 km/s (299,792,458 m/s exactly) in a vacuum. It is a fundamental constant of the universe, denoted "c".

Explanation: Air contains about 78% nitrogen and 21% oxygen.

Explanation: The adult skeleton has 206 bones. At birth, a baby has about 270, but many fuse together during growth.