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The correct answer is Option 3.

Key Points

Concept:

Process of production of Bio-Gas:

• The process involves several stages:
• Firstly, biowaste is crushed into smaller pieces and slurried to prepare it for the anaerobic digestion process.
• Slurrification means adding liquid to the biowaste to make it easier to process.
• Microbes need warm conditions, so the biowaste is heated to around 37 °C.
• The actual biogas production takes place through anaerobic digestion in large tanks for about three weeks.
• In the final stage, the gas is purified by removing impurities and carbon dioxide.
• After this, the biogas is ready for use by enterprises and consumers.

Additional Information

The correct answer is Option 2.

• The heart is made up of four chambers, two on the right and two on the left.
• The upper chambers are the right and left atria.
• Their muscle walls are thin and elastic, and they collect blood coming into the heart.

Key Points

• The lower chambers are the right and left ventricles, which receive blood from the atria above.
• Their muscular walls are thicker than the atria because they have to pump blood out of the heart to various organs of the body.
• Although the left and right ventricle are similar in structure, the walls of the left ventricle are thicker and stronger.
• This is because the left ventricle has to pump blood at a higher pressure so that it reaches all areas of the body but the right side only has to pump blood to the lungs.

Additional Information

The correct answer is Movement of hand.

• Breathing, Heart-pumping, Salivation, Blinking of eyelids etc. is a reflex action.
• Movement of hand is can be both voluntary and involuntary. Hence it can't be a strictly reflex action.

Key Points

• A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus.
• It follows this general sequence and does not involve the brain:
• stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response.
• The nerve pathway followed by a reflex action is called a reflex arc. 
• A receptor in the skin detects a stimulus.
• The sensory neurone sends impulses to the relay neurone.
• The motor neurone sends impulses to the effector.
• Effector produces a response.

Additional Information

The correct answer is Hind-brain.

Key Points

• The Hindbrain is composed of the medulla, the pons, and the cerebellum.
• The Medulla lies next to the spinal cord and controls functions outside conscious control, such as breathing and blood flow.
• The Pons affects activities such as sleeping, waking, and dreaming.
• The Cerebellum controls balance and coordination of movement of the body.
• The cerebellum maintains the posture and equilibrium of the body after getting information from the spinal cord, sensory systems, and other parts of the brain.
• It coordinates the voluntary movements of our body.

Additional Information

The correct answer is Option 4.

Key Points

Litmus solution:

• Litmus solution is generally a purple dye.
• The solution of Litmus is extracted from lichens (these plants belong to the Thallophyta class).
• The Litmus solution is used as an indicator to determine the acidic and basic nature of a solution.
• It has a mauve (purple) colour in distilled water.
• When added to an acidic solution, it turns red.
• When added to a basic solution, it turns blue.

Additional Information

The correct answer is Option 1.

Key Points

Bases:

• A base is a substance that can accept protons or donate a pair of valence electrons to form a bond.
• They are ionic compounds that produce negative hydroxide (OH−) ions when dissolved in water.
• Properties of Base:
• It has a pH value greater than 7.
• Aqueous base solution dissociates into ions to conduct electricity.
• They conduct electricity when dissolved in water.
• It has the ability to accept protons from proton donors.
• It contains OH− ions.
• They form salts when reacting with acids.
• They are bitter to taste if placed in alkali solutions.
• It changes the indicator colour from red litmus paper to blue litmus paper.
• Many bases are insoluble - they do not dissolve in water.
• If a base does dissolve in water, it is called an alkali.

The correct answer is Option 4.

Key Points

• pH is a measure of the concentration of protons (H+) in a solution.
• The concept was introduced by S.P.L. Sorensen in 1909.
• The p stands for the German "Potenz", meaning power or concentration, and the H for the hydrogen ion (H+).
• The "pH" value is an approximate number between 0 and 14 that indicates whether a solution is acidic, basic or neutral.
• At pH 7, the substance or solution is neutral.
• If pH >7, the solution is basic
• If pH < 7, the solution is acidic.
• The pH scale does not have an upper nor lower limit.

Additional Information

The correct answer is Option 4.

Key Points

Refractive defect of vision:

• It means that the shape of our eye does not bend light correctly, resulting in a blurred image.
• Symptoms:
• Blurred vision.
• Difficulty reading or seeing up close.
• Esotropia: Crossing of the eyes in children.
• Defects:
• Myopia (close objects are clear, and distant objects are blurry).
• Hyperopia (close objects are more blurry than distant objects).
• Presbyopia (ageing of the lens in the eye).
• Astigmatism causes blurred vision at all distances**.**

Additional Information

• Cataract:
• A cataract is when your eye's natural lens becomes cloudy. Proteins in your lens break down and cause things to look blurry, hazy or less colourful.

CONCEPT:

Dispersion of light:

• Dispersion of light is the phenomenon of splitting of a beam of white light into its constituent colours on passing through a prism.
• The band of seven colours so obtained is called the (visible) spectrum.
• The dispersion of white light occurs because the colours of white light travel at different speeds through the glass prism.

EXPLANATION:

• As we know, bending of light is inversely proportional to the wavelength of the light.

\(Bending;\alpha ;\frac{1}{{Wavelength}}\)

• Different colours bend differently on passing through a prism and the bending of colour depends on wavelength.

• Higher wavelengths bend less, whereas shorter wavelength bend more.

• Out of all violet has the least wavelength and hence it bends the most and red has the highest wavelength, so it bends the least. Therefore option 2 is correct.

CONCEPT:

• Refraction: The phenomena by which a ray of light bends its path when it travels from one transparent medium to another is called refraction of light.
• The bending happens because the speed of light varies in different mediums.
• Refractive index: The ratio of the speed of light in the air by the speed of light in the medium is called the refractive index. More will be the ratio of refractive index between two mediums more will be the bending of light.
• Atmospheric Refraction: The different layers of the atmosphere have a different refractive index. The ray of light coming from some outer space changes continuously bends its path while passing through different atmospheric layers.

EXPLANATION:

• Stars do not really twinkle, they just appear to twinkle when seen from the surface of Earth.
• The stars twinkle in the night sky due to the atmospheric refraction of starlight.
• When starlight enters our atmosphere it undergoes refraction continuously before it reaches the earth.
• They are affected by winds in the atmosphere and by zones with different temperatures and densities.
• The atmospheric refraction occurs in a medium of gradually changing refractive index.
• Since the atmosphere bends starlight towards the normal, the star's apparent position is slightly different from its actual position.
• The star appears slightly higher (above) than its actual position when viewed near the horizon
• As the path of rays of light coming from the star goes on varying slightly, the starlight's apparent position fluctuates and when it enters, the eye flickers and the star sometimes appears brighter and sometimes fainter, which ultimately results in the twinkling effect.