Explanation

The ozone layer exists about 30 km above the Earth's surface.

It is located in the stratosphere.

It plays a crucial role in blocking harmful ultraviolet radiation from the Sun.

Explanation

• Sputnik 1 was launched by the Soviet Union on October 4, 1957.
• It from the Baikonur Cosmodrome in Kazakhstan, marking the beginning of the space age.
• The successful launch shocked the world and triggered the Space Race between the Soviet Union and the United States.

Explanation

• The principal axis is a horizontal line that passes through the centre of the lens, perpendicular to its surface.
• It is the central axis around which the lens is symmetrical.

Explanation

• A base is a substance that produces hydroxide ions (OH-) in an aqueous solution, making the solution basic.
• Examples of bases include sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2), and ammonium hydroxide (NH4OH).

Explanation

• Acid rain affects the photosynthesis and growth of plants.
• Acid rain can alter soil chemistry and damage leaves, which in turn negatively impacts the photosynthesis process and overall plant health.

Explanation

• Sound travels slowest in air, with a speed of approximately 343 meters per second (m/s) at 20°C.
• This is because air is a gas and has a low density and stiffness, which allows sound waves to propagate more slowly through the material.

The speeds of sound in different materials:

• Air: 343 m/s
• Water: 1433 m/s
• Wood: 3300-3600 m/s
• Brick: 4176 m/s
• Steel: 6100 m/s
• Diamond: 12000 m/s

Explanation

• The number shown above the symbol of an element is called the atomic number (Z).
• It represents the number of protons in the nucleus of an atom.

Explanation

• Asexual reproduction is a type of reproduction where only one parent is involved, and offspring are produced without the fusion of gametes (sex cells).
• This means that the offspring are genetically identical to the parent.

Explanation

• Cross-Pollination is the transfer of mature pollen grains from the anther of one flower to the stigma of a flower on another plant of the same or different species.
• This means that the pollen is transferred between different plants, allowing for genetic diversity and increased fertility.

Explanation

• Transpiration is the process by which water is transported through the plant and evaporates from the aerial parts.
• Such as leaves, stems, and flowers, primarily through small openings called stomata.