Everyday Science

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The salinity of seawater is typically about 3.5%, meaning there are approximately 35 grams of dissolved salts per kilogram (or liter) of seawater. Sodium chloride (common salt) is the major component but constitutes roughly 30 grams per liter, not 1 gram or 10 grams. The question as stated lacks clarity on the volume or mass of seawater considered, and none of the options A (1 gram), B (10 grams), or C (1 kg) correctly represent the typical amount of common salt in a standard amount of seawater. Therefore, the correct answer is D (None of these).

A biosensor is a device that uses biological molecules to detect specific substances. One of the most common applications is measuring blood glucose levels in diabetic patients, making option A correct.

The primary colors in traditional color theory for pigments are red, yellow, and blue. These colors cannot be created by mixing other colors and are used to mix all other colors.

Limestone is a sedimentary rock formed primarily from calcium carbonate deposits, often from marine organisms. It does not belong to igneous or 'hard' rock categories, making 'Sedimentary' the correct classification.

Metamorphic rocks are formed when pre-existing rocks are subjected to great heat and pressure, causing physical and chemical changes without melting. This process alters the original rock into a new type, which is why option C is correct.

The speed of sound in dry air at 20°C is approximately 330 meters per second, which is a well-established physical fact.

The most abundant elements in seawater are sodium and chloride, which combine to form sodium chloride (common salt). These ions are the primary contributors to seawater's salinity.

The age of the Solar System is widely accepted by scientists to be about 4.5 billion years, based on radiometric dating of meteorites and lunar samples.

A mercury thermometer is most suitable for measuring the boiling point of water because mercury has a high boiling point (357°C) and does not evaporate easily at 100°C, providing accurate and stable readings. Alcohol thermometers are less suitable due to alcohol's lower boiling point, and bimetallic thermometers are not typically used for precise temperature measurements like boiling point.

The speed of light in vacuum is approximately 300 million meters per second (more precisely about 299,792,458 meters per second). This is a fundamental physical constant used in many scientific calculations.

The average distance from the Sun to the Earth is approximately 150 million kilometers, which is why option C is correct. This distance is also known as 1 Astronomical Unit (AU).

The standard unit for measuring home electricity energy consumption is the kilowatt hour (kWh), which represents the energy used when a 1-kilowatt device runs for one hour. This unit is commonly used by electricity providers for billing purposes.

Light from the Sun takes approximately 8 minutes and 20 seconds to reach Earth, which is commonly rounded to 8 minutes. This is because the average distance from the Sun to Earth is about 150 million kilometers, and light travels at about 300,000 kilometers per second.

A freely moving magnet aligns itself along Earth's magnetic field because Earth acts like a huge magnet with magnetic north and south poles. This causes the magnet to point towards the geographic north and south directions.

Hematite (Fe2O3) and Magnetite (Fe3O4) are the two most abundant natural iron oxides found in the Earth's crust. Pyrite is an iron sulfide, and bauxite is an aluminum ore, so they are not iron oxides.