Explanation

Priestly discover oxygen in 1776.

Oxygen makes up about 46-50% of the Earth's crust by weight, mainly in the form of oxides and silicates.

It is also a major component of water (H₂O).

It is abundant in the atmosphere as O₂.

Explanation

Decomposers are organisms that break down dead or decaying organisms; they carry out decomposition, a process possible by only certain kingdoms, such as fungi.

Explanation

Mangrove forests act as barriers against cyclones.

Mangroves reduce erosion by trapping sediments, stabilizing the coastal zone and thus protecting the coast from storm surges and cyclones.

Mangroves in Pakistan are found along the coastline of Sindh and Balochistan.

Explanation

 Rainbows occur when sunlight is refracted, reflected, and dispersed in water droplets, creating a spectrum of colors.

When light meets a water droplet,

It is refracted at the boundary of air and water, and enters the droplet

Where the light is dispersed into the seven colors

Explanation

Sunlight is composed of the following seven colours:

1.       Violet

2.       Indigo

3.       Blue

4.       Green

5.       Yellow

6.       Orange

7.       Red

Explanation

• Ozone gas is a molecule made up of three oxygen atoms, with the chemical formula O3.
• This is different from ordinary oxygen, which has the chemical formula O2.

Explanation

• A parasite is an organism that feeds and lives in or on part of another organism (host), often causing harm to the host.
• In this case, the mosquito is feeding on the human's blood, making it a parasite.

Explanation

Petroleum, natural gas & coal are called non-renewable energy sources.

The most popular renewable energy sources currently are:

1.      Solar energy

2.      Wind energy

3.      Hydro energy

4.      Tidal energy

5.      Geothermal energy

6.      Biomass energy

RK12-12-2022

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

Air is a homogeneous mixture of the gaseous substances

nitrogen,

oxygen, 

smaller amounts of other substances.