Nitrogen comprises about 78% of Earth's atmosphere, followed by oxygen at about 21%.

The Sun is the primary source of energy for Earth, providing energy through radiation that drives weather, climate, and photosynthesis.

Melting of ice is a physical change as water remains H₂O but changes from solid to liquid state. Other options are chemical changes.

Newton's third law states that for every action, there is an equal and opposite reaction. Forces always occur in pairs.

The liver is the largest internal organ by mass, weighing approximately 1.5 kg in adults.

Ice has lower density than water, which is why ice floats on water. Water expands when it freezes.

A turbine is not a simple machine. The six simple machines are lever, pulley, inclined plane, wedge, screw, and wheel-axle.

Methane (CH4) is the primary component of natural gas, making up about 70-90% of its composition.

Red blood cells (erythrocytes) contain hemoglobin and transport oxygen from lungs to body tissues.

Freezing is the phase change from liquid to solid, typically occurring at the freezing point of a substance.