VARDAAN LEARNING INSTITUTE

Sodium metal is very reactive. It reacts vigorously with oxygen and water. To prevent this accidental fire, it is kept immersed in kerosene.

Lightning: It is a huge electric discharge that occurs between clouds or between a cloud and the ground.
Cause: It occurs due to the accumulation of charges in clouds. When negative charges from the clouds meet positive charges on the ground (or other clouds), lightning strikes.

Audible Sound: Sounds having frequency between 20 Hz to 20,000 Hz. Humans can hear these.
Inaudible Sound: Sounds with frequency below 20 Hz or above 20,000 Hz. Humans cannot hear these.

When a body rolls, the area of contact is very small compared to sliding. Rolling friction is much smaller than sliding friction because less force is required to overcome the interlocking of irregularities.

Zygote: It is a single cell formed by the fusion of male and female gametes.
Foetus: It is a multicellular stage of the embryo where all body parts can be identified.
OR
Metamorphosis: The transformation of the larva into an adult through drastic changes is called metamorphosis. Examples: Frog (Tadpole to Frog), Silkworm (Caterpillar to Moth).

Antibiotics: Medicines that kill or stop the growth of disease-causing microorganisms (bacteria).
Precautions: (1) Should be taken only on the advice of a qualified doctor. (2) Complete the course prescribed.

Formation of Coal: Millions of years ago, dense forests got buried under the soil due to natural processes like flooding. As more soil deposited over them, they were compressed. Under high temperature and high pressure, dead plants slowly got converted to coal.
Process: This process is called Carbonisation.

Conditions for Combustion:
1. Presence of a combustible substance (fuel).
2. Presence of a supporter of combustion (oxygen/air).
3. Attainment of ignition temperature.

Advantages: Economical use of water, prevents water wastage, useful for uneven land / scantly water regions.
Methods:
1. Sprinkler System: Useful for uneven land and sandy soil.
2. Drip System: Water falls drop by drop near roots; best for fruit plants/gardens.

(Draw a labelled diagram of Human Eye showing parts: Cornea, Iris, Pupil, Lens, Retina, Optic Nerve).
OR
(a) Iris: Controls the size of the pupil.
(b) Retina: Acts as a screen where the image is formed.
(c) Ciliary muscles: Hold the lens and adjust its focal length.

(a) Dholak: Stretched membrane.
(b) Sitar: Stretched string.
(c) Flute: Air column.

A charged balloon repels another charged balloon because like charges repel each other. An uncharged balloon is attracted by a charged balloon because a charged body induces an opposite charge on the near surface of the uncharged body (Induction), leading to attraction.

Acid Rain: Pollutants like sulphur dioxide and nitrogen dioxide react with water vapour in the atmosphere to form sulphuric acid and nitric acid. This falls as acid rain. Acid rain reacts with the marble (Calcium Carbonate) of Taj Mahal, causing it to corrode and turn yellow. This phenomenon is called 'Marble Cancer'.

(a) Menarche: The first menstrual flow at puberty. Menopause: Stoppage of menstruation around 45-50 years of age.
(b) Sex is determined by sex chromosomes. Males have XY, Females having XX. If a sperm carrying X fertilizes the egg (X), it's a girl (XX). If Y sperm fertilizes egg, it's a boy (XY).
OR
(a) Adolescence: The period of life when the body undergoes changes leading to reproductive maturity.
(b) Boys: Facial hair, Deep voice, Broad shoulders.
Girls: Breast development, High pitched voice, Widening of hips.

(a) Force: Push or pull on an object. Examples: Kicking a ball, Lifting a book.
(b) Forces on Rocket:
1. Gravitational Force: Acting downwards (Weight).
2. Frictional Force (Drag): Due to air, acting downwards against motion.

(a) To reduce friction between the striker/coins and the board surface for smooth movement.
(b) To increase friction (grip) with the ground so they don't slip while running.
(c) Necessary Evil: Friction is necessary because without it we cannot walk, write, or stop vehicles. It is 'evil' because it causes wear and tear of machine parts and energy loss as heat.

(i) Carrots, Spinach, Milk, Eggs, Cod liver oil, Papaya. (Any two)
(ii) Night blindness.
(iii) (1) Wash eyes with cold water. (2) Do not read in dim light.

(i) Water conducts electricity and can cause electric shock to the person fighting the fire.
(ii) Carbon dioxide (CO₂).
(iii) It cuts off the supply of air (oxygen) to the fire, thus extinguishing it.

(i) Budding.
(ii) Clone: An organism which is genetically identical to its parent.
(iii) In Budding (e.g. Hydra), a small outgrowth (bud) detaches to form a new individual. In Binary Fission (e.g. Amoeba), the parent body divides into two equal halves.