Everyday Science

The Mohs scale is a scale of mineral hardness used to measure the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. Therefore, it is used to measure hardness.

Vitamins A, D, E, and K are the four fat-soluble vitamins. Vitamins B and C are water-soluble, and 'AOT' is not a vitamin. Therefore, the correct answer is Vitamin K.

Perspiration primarily helps regulate body temperature by releasing sweat, which cools the body as it evaporates. This is the main physiological function of sweating.

Uranus is the coldest planet in the solar system because it has the lowest average temperature, around -224°C, due to its great distance from the Sun and lack of internal heat. Earth, Venus, and Mercury are all warmer planets.

A solar eclipse occurs when the Moon passes between the Earth and the Sun, blocking the Sun's light either partially or completely. This alignment causes the Sun to be obscured from view on Earth.

A fathom is a unit of length commonly used to measure the depth of water and is equal to 6 feet. This is a standard measurement in nautical contexts.

Police officers commonly use radar guns that emit radio waves to measure the speed of approaching vehicles. The radio waves reflect off the car, and the change in frequency is used to calculate speed.

The three elements with the highest percentage by mass in the human body are oxygen (~65%), carbon (~18.5%), and hydrogen (~10%). Calcium is much less abundant, about 1.5%. Therefore, carbon is the element with the third highest percentage in the human body after oxygen and hydrogen. The option stating calcium at 75% is incorrect and not supported by scientific data.

Vitamin D deficiency leads to poor calcium absorption, causing bone diseases such as osteoporosis and increased risk of fractures.

Potassium nitrate is commonly used as a fertilizer because it provides essential nutrients like potassium and nitrogen to plants, promoting healthy growth.