Explanation

The most abundant gas in the atmosphere is nitrogen, with oxygen second.

Argon, an inert gas, is the third most abundant gas in the atmosphere.

Explanation

Because sound is just vibrating air, space has no air to vibrate and therefore no sound in a vacuum.

Sound waves below 20 Hz are known as infrasound.

Sound waves above 20 kHz are known as ultrasound

Sound waves transmit a medium such as a gas, liquid, or solid.

• The speed of sound in air is about 343 meters per second
• The sound travels at 1,481 m/s in water 
• The speed of sound in a vacuum is zero meters per second.

Explanation

• The scientist who first discovered that the earth revolves around the sun was Copernicus.
• Earth's Rotational Theory:
  • Rotation can be defined as the spin of Earth on its own axis from west to east direction.
  • It must also be noted that the speed of rotation of the earth is not constant throughout latitudes.
    
  • It differs at different latitudes.

Explanation

Geothermal, Solar, and Hydropower all come from naturally replenished sources.

These energies are renewable because they do not deplete with use and are environmentally friendly.

Renewable sources of energy include:

• Solar energy
• Wind energy
• Hydropower
• Geothermal energy
• Biomass

Explanation

• The most abundant component in Earth's atmosphere is nitrogen, making up about 78% of the air.
• The second most abundant gas is oxygen, which makes up about 21% of the air.
• Hydrogen and carbon dioxide are both present in the air, but in much smaller amounts than nitrogen and oxygen.