CONCEPT:

• Dispersion of light: The phenomenon in which a white light ray when falls on a prism get separated into its component colors is called dispersion of light.
• Primary rainbow: Primary rainbow is the result of One Total internal reflection and two refractions from the suspended raindrop.
  • Violet color forms on the inner edge and red color on the outer edge. Angles subtended with the direction of sun are 42˚ (red) and 40˚ (violet) above the horizon.
  • The primary rainbow is a result of a three-step process, that is, refraction, reflection, and refraction.

• Secondary Rainbow: Secondary rainbow is the result of two total internal Reflections (TIRs) and two refractions from the suspended raindrop.
  • In this rainbow red color appears on the inner edge while violet color appears on the outer edge which is reverse of that of primary rainbow.
  • This is because of additional reflection which causes 180˚ phase shift.

EXPLANATION:

• In case of a primary rainbow, the ray of light suffers refraction twice and reflection once in the water droplet. So option 1 is correct.

Concept:

Convex lens is converging lens which means it converges the light falling on it to one point.

The lens formula is

where v and u is image and object distance from the lens. f is the focal length of the lens.

Calculation:

Using lens formula for first refraction from convex lens

Thus the final image is virtual and at a distance,

60 – 40 = 20 cm from plane mirror

Concept:

Newton’s third law of motion:

• “To every action, there is always an equal and opposite reaction”.
• Action and reaction forces act on different bodies, not on the same body.
•  Force on a body A by B is equal and opposite of the force on the body B by A.

Force on A by B = – Force on B by A

F_AB = - F_BA

Explanation:

• Horse will apply the pull force on the cart.
• Cart applies pull force on horse just opposite to force applied by horse on cart.
• To move forward, the horse will push the ground in opposite to the desired motion.
• According to Newton's law, ground will apply the same magnitude of force to the horse in the forward direction.

From the above discussion, we can conclude that, the horse  moves forward due to the force which the ground exerts on the horse.

CONCEPT:

• Free fall is the vertical descent of a body in which acceleration due to gravity is the only force acting on it.
• Equations of motion give the idea about characteristics of motion such as velocity, acceleration, and displacement.
• Under the influence of gravity or free fall the equations of motion changes to

V = U + gt

V² = U² + 2gh

Where U = initial velocity, V = final velocity, g = acceleration due to gravity, t = time, and h = height/distance covered

CALCULATION

Given  - Initial velocity (U) = 29 ms^-1, and t =10 sec

• The displacement of stone which is thrown vertically upwards is given by

Concept:

As the body is moving with constant velocity so forces acting on the body must be balanced.

⇒ Contact force from incline should balance weight of the body.

|F_contact| = Mg

∴ The magnitude of the contact force is Mg.

Key Points

• A good or valuable fuel has a low ignition temperature and a high calorific value.
• Good fuels have a high calorific value, which means that the energy released when a specific amount of fuel is heated is greater.
• The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/kg).
• Good fuels have a low ignition temperature (the lowest temperature at which a substance catches fire).
• A good fuel is one which is readily available. It is cheap. 
• It burns easily in air at a moderate rate. It produces a large amount of heat. It does not leave behind any undersirable substances.

Mistake Points

According to the answer key answer is option D, but we have taken the reference of the NCERT book, so according to that option A is  correct one.

The correct answer is Bitumen, Coal Tar

Concept:-

• Source and Derivation: Identifying substances based on their source—whether they are derived from petroleum or coal—is crucial. This differentiation helps in understanding their properties, uses, and how they are processed.
• Physical State: Recognizing the physical state (solid, liquid, gas) of a substance and its relevance to its described use, such as in road construction where a liquid or viscous material is required.
• Industrial Application: Knowledge of how certain materials are used in industry, particularly in construction and manufacturing, aids in identifying substances based on their described uses.
• Byproducts of Processes: Understanding the byproducts of industrial processes (like the coking of coal or the distillation of crude oil) allows us to connect substances with their sources.

Explanation:-

• X and Y are described as thick, black liquids used for metalling roads, indicating their use as binding agents in road construction for asphalt and similar applications.
• Petroleum and Coal Derivation: The description specifies that X is derived from petroleum and Y from coal. This clue is essential for identifying the substances correctly.
• Bitumen is a viscous liquid commonly used in road construction and waterproofing. It is refined from crude oil, making it a petroleum-derived product. Given its properties and applications, Bitumen fits the description of X.
•  Coal Tar is a byproduct of the coal coking process, used in producing coke or gasified to produce coal gas. It is a thick, black liquid, used in industrial and medical applications, and also in sealing roads. Coal Tar matches the description of Y, as it is derived from coal.
• Charcoal is not a liquid; it's a porous form of carbon obtained from the carbonization of wood or other organic materials. Therefore, any option listing charcoal as either X or Y can be disregarded.

Conclusion:-

Given the descriptions and the process of elimination based on the provided concepts, the correct answer is Bitumen, Coal Tar

Key Points

• The pH value of salts of strong acid and strong base is 7.
  • The salts are from a strong acid and strong base that do not hydrolyze and the resulting salt pH will remain 7.
  • The anion in the salt form's strong base does not attract the H+ from the water.
• Salt of a strong acid and a weak base is acidic with a pH value less than 7 because acid is strong which retains the pH value less than 7. Statement I is correct
• Salt of a weak acid and strong base is base with a pH value of more than 7 because the base is strong hence pH of the whole solution will be more than 7.
• Salt of a strong acid and strong base is neutral because both are strong and cancels strong effects of each other, the pH will be 7.

Statement II:(Incorrect)

• When electricity is passed through an aqueous solution of sodium Chloride (brine), it decomposes to form NaOH + H₂ + CI₂.
• Brine is a saturated solution of NaCl (Sodium chloride).
• Electrolytic decomposition of solution gives Cl₂ (Chlorine) at the anode and H₂ (Hydrogen) is formed at the cathode and NaOH (Sodium hydroxide ) is formed near to the cathode.
• This process is known as chor- alkali process.

Explanation:

Gases:

• Gases have expanding nature and completely fill their containers.
• Gases take the shape of their containers.
•  They are compressible by nature.
• Mixtures of gases are always homogeneous.
• They have low density.
• Gases can be mixed easily.
• Most of the oxides are gaseous in nature.
• Hydrogen, carbon. sulphur, nitrogen, phosphorus are found in the gaseous state in nature.

Petrochemicals:

• Petrochemicals are chemical substances that are derived from petroleum and natural gas.
• Example- Propylene, Ethylene, Butadiene, etc.
• They are used for medical, household, clothing and other purposes.
• They are also used in the making of paints and building materials.

Acid Rain:

• It is the process of forming acidic components while the precipitation of rain.
• Sulphuric and nitric acids are commonly found in acid rains.
• Acid rain is also called acid deposition.
• This acidic rain has an acidic pH value (0-7).
• This can take the form of rain, snow, fog, hail, etc.

Explanation:-

(a) Generally non-metals do not react with water. This statement is correct because non-metals typically lack the ability to donate electrons to hydrogen in the water, which would be necessary to replace the hydrogen and form a hydroxide. Their chemical properties do not favor the kind of displacement reaction that metals often engage in with water.

(b) Generally non-metals do not react with acids. This statement is also correct. Non-metals usually do not react with acids in a way that metals do because reactions between metals and acids often involve the metal displacing hydrogen from the acid to form a salt. Since non-metals are not keen to lose electrons (as opposed to metals which can more easily donate electrons to the hydrogen ions in the acid), they generally do not engage in similar displacement reactions with acids.

Therefore, both statements (a) and (b) correctly describe general tendencies in the reactive behaviors of non-metals with water and acids, respectively.

Conclusion:-

So,  the correct statements are Both (a) and (b)