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The correct answer is 30°.

Concept:

Reflection:

• The bouncing back of light rays after they hit a surface is known as reflection of light.
• After striking the mirror, the ray of light is reflected in another direction.
• The light ray, which strikes any surface, is called the incident ray.
• The ray that comes back from the surface after reflection is known as the reflected ray.
• The angle between the normal and incident ray is called the angle of incidence (∠i).
• The angle between the normal and the reflected ray is known as the angle of reflection (∠r)
• Two laws of reflection are
• (i) The angle of incidence is equal to the angle of reflection.
• (ii) Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.

Explanation:

Law of reflection-  The angle of the reflected ray is equal to the angle of the incident ray with respect to the normal to the surface, that is to a line perpendicular to the surface at the point of contact.

Given:

Angle of incidence = 30°

According to the Law of Reflection,

θ_i = θ_r

where, θ_i is angle of incidence 

θ_r is angle of reflection.

Hence, Angle of Reflection = 30°

The correct answer is 100.

Concept:

Frequency (f):

• The number of waves that pass a given point per second is called frequency.
• Frequency is usually represented by f.
• The SI unit of the Frequency is hertz (Hz).

Time period:

• The time taken to complete one full oscillation or cycle by the Wave is called the time period.
• It is represented by the symbol t.
• The SI unit of the time period is second (s).

The relationship between time period and frequency is given as:

Time Period \((t) = \frac{1}{f}\)

Explanation:

Given that:

Frequency (f) = 50 Hz

Time Period (t) = 2 sec.

The number of vibrations = frequency x time period

= 50 x 2 = 100 vibrations

Hence, the correct answer is 100.

The correct answer is All of these.

Explanation:

Light-emitting diode (LED)

• The light-emitting diode (LED) is a commonly used standard light source in electrical equipment.

• It can be used for anything from your mobile phone to large advertising billboards.

• They are mostly found in devices that display time and various types of data.

• When an electric current flows through a light-emitting diode (LED), the device emits light.

• When current flows through an LED, electrons recombine with holes, resulting in the emission of light.

• LEDs allow current to flow in one direction but prevent it from flowing in the opposite direction.

• Light-emitting diodes are p-n junctions that have been heavily doped.

• When forward biassed, an LED will emit coloured light at a specific spectral wavelength depending on the semiconductor material used and the amount of doping.

• An LED is encapsulated with a transparent cover, so that the emitted light can be seen.

• LEDs can emit red, yellow, orange, green and blue light.

The correct answer is satellite.

Explanation:

• The Sun and the celestial bodies which revolve around it form the solar system.
• It consists of large number of bodies such as planets, comets, asteroids and meteors.
• The gravitational attraction between the Sun and these objects keeps them revolving around it.

Satellite

• A satellite is any celestial body that revolves around another celestial body. Thus, the satellite is not a member of the solar system.
• Natural satellites and artificial satellites are the two types of satellites.
• For example, the Moon revolves around the Earth in a fixed orbit, so it is a satellite of the Earth. As a result, the Moon is an example of a natural satellite.
• A celestial body is said to be a satellite of another celestial body if and only if the other celestial body is a planet.
• For example, because the Moon revolves around the Earth and the Earth is a planet, the Moon is a satellite of the Earth.
• Although the earth is a satellite of the sun, it is more commonly referred to as a planet of the sun.

Asteroids

• Apart from the stars, planets and satellites, there are numerous tiny bodies which also move around the sun.
• These bodies are called asteroids.
• They are found between the orbits of Mars and Jupiter.

Meteors 

• The small pieces of rocks which move around the sun are called meteoroids.
• Sometimes these meteoroids come near the earth and tend to drop upon it.
• During this process due to friction with the air they get heated up and burn.
• It causes a flash of light. Sometimes, a meteor without being completely burnt, falls on the earth and creates a hollow.

Comets 

• Comets are also members of our solar system.
• They revolve around the Sun in highly elliptical orbits.
• However, their period of revolution round the Sun is usually very long. A Comet appears generally as a bright head with a long tail.
• The length of the tail grows in size as it approaches the sun.
• The tail of a comet is always directed away from the sun. Many comets are known to appear periodically.
• One such comet is Halley’s comet, which appears after nearly every 76 years. It was last seen in 1986.

The correct answer is Learning by doing.

• The teaching method is a technique for putting theory into practice.
• The method of teaching refers to the process of interpreting the world of knowledge into the mind of a student.
• It assists teachers in understanding "what to teach," "how to teach," and "how to approach it." It includes both teaching strategies and techniques, as well as the selection of what is to be taught.

Key Points

• The laboratory method is a modern teaching method that is primarily used in mathematics and science.
• In the laboratory method, students conduct laboratory experiments with their own hands-on laboratory exercises in small groups.
• This method allows students to become acquainted with the facts through direct experiences.
• The students themselves validate the theoretical knowledge through experiments, which provide a solid foundation for their learning.
• This method is based on the psychological principle of learning by doing, with an emphasis on hands-on activities that provide students with direct and concrete experiences.
• All experiments and activities in science can be carried out in the laboratory, which is equipped with scientific equipment and other useful teaching aids.
• Hence, the Laboratory method is based on learning by doing.

Additional Information

Advantages of the Laboratory Method

1. Students must discover qualitative or quantitative solutions to their problems.
2. Students learn best through the 'learning by doing method.
3. It takes a child-centered approach.
4. It encourages students to be active and alert.
5. It teaches scientific methodology.
6. The knowledge becomes clear and permanent as it provides concrete and direct self-experiences.
7. Students gain practical knowledge and proficiency in the use of scientific apparatus and equipment.

The correct answer is Nylon.

Concept:

The term "fibre" refers to a thin thread made from either natural or artificial materials, particularly one used to make cloth or rope.

Synthetic fibre

• Synthetic fibres are those that are not derived from natural sources such as plants and animals.
• Synthetic fibres are either modified natural fibres or produced directly in laboratories.
• The synthetic fibres are made by human beings.
• These are called synthetic or man-made fibres.
• A synthetic fibre is also a chain of small units joined together. Each small unit is actually a chemical substance.
• Many such small units combine to form a large single unit called a polymer.
• Synthetic fibre is more durable than natural fibre.

Natural fibre

• Cotton is a fluffy fabric made of cellulose, an insoluble substance, and is one of the most common fabrics used today to manufacture clothing materials.
• Natural fibres can be derived from both plants and animals.
• They are typically processed and spun into yarn, which is then turned into a product.
• Because of their physical properties, natural fibres such as cotton are preferred for clothing materials.
• They are typically soft and lightweight, making them a popular textile type.
• Cotton, wool, silk, and other natural fibres are derived from plants or animals.

Explanation:

Nylon

• Nylon was created without the use of any natural raw materials (from plants or animals).
• It was made from coal, water, and air.
• It was the first fully synthetic fibre.
• Nylon fibre was strong, elastic, and light. It was lustrous and easy to clean.
• As a result, it became very popular for making clothes.
• It is the strongest synthetic fibre and can be moulded into any shape.
• It is simple to dye but does not absorb water well.
• Because it is elastic, it is extremely durable.
• It is highly resistant to oil, grease, moths, fungus, and a variety of other pests.
• Because it can be shaped into any shape, it can be made into palettes and even powder.
• It is used to make thread, reel thread, ropes, seatbelts, sarees, tracksuits, raincoats, fishing nets, swimming wears, sleeping bags, and other items due to its many properties.

The correct answer is K.

Key Points

• Potassium is a chemical element with the atomic number 19 and the symbol K (from Neo-Latin kalium).
• Potassium is a silvery-white metal that can be cut with a knife with little effort. They have low melting points and low densities.
• In seconds, potassium metal reacts with atmospheric oxygen to form flaky white potassium peroxide.
• It was first isolated from potash, or plant ashes, from which it gets its name.
• The electronic configuration of potassium is [Ar] 4s¹.
• In the periodic table, potassium is an alkali metals, which all have a single valence electron in the outer electron shell that is easily removed to form an ion with a positive charge - a cation - that combines with anions to form salts.
• In nature Potassium occurs only in ionic salts.
• Potassium ions are required for all living cells to function properly.
• Uses of potassium:
• It is used as a heat exchange medium and in nuclear power plants.
• Potassium salts are a component of fertiliser.
• It is one of the most important nutrients for the human body.
• Potash can be used to make glass, soap, and a variety of other products.
• Physical and Chemical Properties of Potassium:
• It is a silky, lustrous metal and a melting point of 63°F and a boiling point of 770°F.
• Potassium is a metal that can float in water.
• It has a lavender-coloured flame and green smoke.
• It is the seventh most common element in the crust of the world.
• Potassium is a malleable metal with a silver colour profile once isolated.
• Potassium interacts aggressively with water, releasing hydrogen gas.​

Additional Information

Phosphorus is a chemical element with symbol P and the atomic number 15.

Polonium is a chemical element with symbol Po and the atomic number 84.

Platinum is a chemical element with symbol Pt and the atomic number 78.

The correct answer is Al (NO3)3.

Key Points

• Aluminium nitrate is a white, water-soluble salt of aluminium and nitric acid that is most commonly found as a crystalline hydrate.
• The chemical formula of aluminium nitrate is Al (NO₃)₃.
• Aluminium nitrate is produced by neutralising dilute nitric acid with aluminium (III) chloride or any of the aluminium salts such as aluminium hydroxide.

3HNO₃ (dilute) + AlCl₃ → Al(NO₃)₃ + 3HCl 

• Aluminium nitrate is also known as Nitric aluminium salt and aluminium (III) nitrate.
• Uses of Aluminium Nitrate are
• Used as a strong oxidising agent
• Used in the extraction of uranium
• Used as a corrosion inhibitor
• Used in transformer core laminates
• Used in the refining of petroleum
• Used in tanning leather

Additional InformationProperties of Aluminium Nitrate

The correct answer is Mixture of grain and husk.

Concept:

Separation of substances

• Substances are separated from the mixture in process of removing impurities or obtaining useful substances out of the mixture.
• Some common examples of separations include the separation of salt from seawater, butter from milk, grain from stalks, etc.
• Different methods of separations are handpicking, threshing, winnowing, and sieving.

Explanation:

Winnowing:

• Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air.
• This method is commonly used by farmers to separate lighter husk particles from heavier seeds of grain.
• The husk particles from the grain are carried away by the wind or by blowing air.
• The seeds of grain get separated and form a heap near the platform for winnowing.
• The separated husk is used for many purposes such as fodder for cattles.

Additional Information

Handpicking:

• The method of handpicking is used to separate undesirable substances such as small pieces of stones from wheat, and rice.
• The quantity of such impurities is usually not very large.
• In such situations, we find that handpicking is a convenient method of separating substances.
• Some common examples are the Separation of pebbles from grain, and the Separation of pebbles from wet sand, etc.

Threshing:

• The process that is used to separate the grain from stalks etc. is threshing.
• In this process, the stalks are beaten to free the grain seeds.
• Sometimes, threshing is done with the help of bullocks.
• Machines are also used to thresh large quantities of grain.

Sieving:

• Sieving allows the fine flour particles to pass through the holes of the sieve while the bigger impurities remain on the sieve.
• In a flour mill, impurities like husk and stones are removed from wheat before grinding it.
• Usually, a bagful of wheat is poured into a slanting sieve.
• The sieving removes pieces of stones, stalk, and husk that may still remain with wheat after threshing and winnowing.

The correct answer is Phenolphthalein.

Explanation:

Synthetic indicators 

• Synthetic indicators are acid-base indicators made from artificial substances.
• They are created in laboratories.
• Examples of Synthetic indicators-
• Phenolphthalein:
• Phenolphthalein is a synthetic indicator that is colourless in acidic solutions but pink in basic solutions.
• It is most commonly used in acid-base titrations.
• Methyl orange:
• ​In acidic medium, methyl orange appears red; in basic medium, it appears yellow.

Additional Information

Natural indicators

• T he acid-base indicators obtained from natural sources are known as natural indicators.
• Examples of  Natural indicators-
• Litmus 
• Litmus is the most widely used natural indicator.
• It is derived from lichens.
• It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue.
• It turns red when added to an acidic solution and blue when added to a basic solution.
• It is available as a solution or in the form of strips of paper known as litmus paper.
• It is typically available in red and blue litmus paper.
• Turmeric
• The colour of turmeric does not change in acidic medium, but it changes from yellow to deep red in basic medium.
• China rose petals (Gudhal)
• China rose indicator turns acidic solutions to dark pink (magenta) and basic solutions to green.