✓ (iv) 46 — Human skin cells are somatic (body) cells and contain the full diploid number of chromosomes: 46 chromosomes (23 pairs). Only gametes (sperm and egg) have 23 (haploid).

✓ (iii) P = 1/f — Power of a lens P = 1/f (where f is focal length in metres). Rearranging gives f = 1/P. This is the correct formula to find focal length from power (in dioptres). The lens formula is 1/v − 1/u = 1/f.

✓ (iv) Tricuspid valve — The tricuspid (right atrioventricular) valve is located between the right atrium and right ventricle. It prevents backflow of blood from the right ventricle into the right atrium during ventricular contraction.

✓ (iv) तुलसी (Holy Basil) — Tulsi (Ocimum tenuiflorum) has strong antimicrobial properties and is traditionally used to activate the digestive process. It also helps in treating respiratory diseases and boosting immunity.

✓ (ii) Ethylene glycol (इथिलिन ग्लाइकोल) — Di-hydric alcohols have two –OH groups. Ethylene glycol (HOCH₂–CH₂OH) has exactly 2 –OH groups. Ethanol and methanol are monohydric (1 –OH); glycerol is trihydric (3 –OH).

✓ (i) Increases (बढ्छ) — g = GM/R². If Earth's mass (M) stays constant but radius (R) decreases to Moon's size, then g increases because g ∝ 1/R². Smaller R → much larger g. (Earth would become a very dense object with very strong surface gravity.)

✓ (i) Electric motor changes electrical energy into kinetic (mechanical) energy — An electric motor converts electrical energy → mechanical energy. A generator does the opposite. They work on opposite principles (motor: current-carrying conductor in magnetic field; generator: electromagnetic induction).

✓ (iv) Nature of matter (पदार्थको प्रकृति) — Specific heat capacity is an intrinsic property that depends only on the nature (type/substance) of matter, not on its mass, volume, or temperature. Water has c = 4200 J/kg°C, iron has c = 460 J/kg°C regardless of their amounts.

✓ (iii) kg m²s⁻² — Joule = work = force × distance = (kg·m/s²) × m = kg·m²·s⁻². This is also equivalent to the unit of kinetic energy: ½mv² → kg·(m/s)² = kg·m²·s⁻².

✓ (i) 875 N — Pascal's Law: F₁/A₁ = F₂/A₂
500/200 = F₂/350
F₂ = 500 × 350/200 = 500 × 1.75 = 875 N

(a) Artery (धमनी) — Arteries carry oxygenated blood from the heart to all parts of the body (except pulmonary artery which carries deoxygenated blood to the lungs).

(b) Ammonium hydroxide / Ammonia solution (NH₄OH) — NH₃ + H₂O → NH₄OH (ammonium hydroxide, also called aqueous ammonia).

(c) CO₂ is denser (heavier) than air. When collected in an erect jar, the denser CO₂ settles at the bottom and pushes lighter air upward, allowing efficient gas collection by downward displacement of air.

(d) A good netizen should: protect personal information/privacy online; avoid sharing unverified information (fake news); use strong passwords; be respectful in online communication. (Any one precaution is acceptable.)

(e) A negative catalyst decreases (slows down) the rate of chemical reaction by increasing the activation energy or by an alternative mechanism that inhibits the reaction.

(f) Detergents are made from petroleum-based chemicals that are non-biodegradable. They persist in the environment, cause water pollution, and harm aquatic life, unlike soap which is biodegradable.

(g) F₁ cross: Bb (black) × bb (brown) → F₁: 1Bb : 1bb (1 Black : 1 Brown)
F₁ × F₁ (Bb × Bb): F₂ genotypic ratio = 1BB : 2Bb : 1bb (Phenotype: 3 Black : 1 Brown)

(h) The student has Myopia (nearsightedness). Ray diagram of correction:

Distant object → Concave (diverging) lens → Eye lens → Image on Retina ✓
      ↓ diverges rays ↓
 (Without lens image would form IN FRONT of retina — myopia)
 Concave lens shifts image back to retina.

Corrected with a concave lens of suitable negative power.

(i) μ = speed in air / speed in water = (3×10⁸) / (2.25×10⁵)
Note: Question likely intends 2.25×10⁸ m/s (standard value for light in water).
μ = (3×10⁸) / (2.25×10⁸) = 3/2.25 = 1.33 (refractive index of water)

1. Worker bees are the smallest in size and are all sterile females (diploid, 2n = 32). They cannot reproduce under normal conditions.

2. They have specialized structures: pollen baskets (corbicula) on hind legs for collecting pollen, wax glands for building honeycomb, and a stinger (modified ovipositor) for defense of the colony.

1. Melting of glaciers and rising sea levels: Global warming causes polar ice caps and glaciers to melt, leading to rising sea levels that threaten low-lying coastal areas and islands with flooding.

2. Extreme weather events: Climate change leads to more frequent and intense extreme weather — droughts, floods, hurricanes, and heat waves — disrupting agriculture, ecosystems, and human settlements.

Independent Variable	Dependent Variable
The variable that is deliberately changed or controlled by the experimenter.	The variable that changes as a result of the independent variable; it is measured/observed.
It is plotted on the X-axis (horizontal axis) of a graph.	It is plotted on the Y-axis (vertical axis) of a graph.

Example (Q18i): Amount of sunlight = independent variable; growth of plant = dependent variable.

Sparrow (भँगेरो): Class — Aves (Birds). Sparrows are warm-blooded vertebrates with feathers, hollow bones, and wings; they lay eggs and belong to Phylum Chordata, Class Aves.

Fern (उनिउ/फर्न): Division — Pteridophyta. Ferns are vascular plants that reproduce via spores (no seeds or flowers). They have well-developed roots, stems, and leaves (fronds).

1. Long generation time: Apple trees take several years to produce fruit, while pea plants complete their life cycle in one growing season. Mendel's experiments over generations would have taken decades instead of years.

2. Complex traits and cross-pollination difficulty: Apples have a complex genetic makeup with many contrasting characters that are hard to track. Also, controlling pollination in apple trees (which are large) is difficult compared to pea flowers that can be easily hand-pollinated or self-pollinated.

16 N represents the apparent weight / tension in the spring balance — It is the weight of the object as measured while it is submerged in water. The spring balance reads less than the actual weight because the water exerts an upward buoyant force on the object.

For the object to float: The object must be placed freely in water (not attached to the balance). For floating, Weight of object = Buoyant force = Weight of water displaced. In this case, the apparent weight (16 N) + buoyant force = actual weight. For floating, the actual weight must equal the buoyant force, so the object would need to have a weight equal to the weight of water it displaces — the object floats when its density ≤ density of water.

Flat Universe (समतल ब्रह्माण्ड)	Closed Universe (वन्दं ब्रह्माण्ड)
The universe has zero curvature; it is infinite and expands forever at a declining rate.	The universe has positive curvature (like a sphere); gravity is strong enough to eventually halt expansion and cause it to collapse (Big Crunch).
Parallel lines remain parallel; density equals the critical density (Ω = 1).	Parallel lines converge; density is greater than the critical density (Ω > 1).

(i) Reaction A (MgO + H₂O → Mg(OH)₂) is the combination reaction — Two reactants (MgO and H₂O) combine to form a single product Mg(OH)₂. This is the definition of a combination (synthesis) reaction: A + B → AB.

(ii) When concentrated H₂SO₄ is used instead of dilute H₂SO₄ with zinc: Concentrated H₂SO₄ acts as an oxidizing acid. Instead of producing H₂ gas, it produces SO₂ gas (sulphur dioxide). The reaction becomes:
Zn + 2H₂SO₄ (conc.) → ZnSO₄ + SO₂↑ + 2H₂O
So no hydrogen gas is evolved; SO₂ is produced instead.

Reaction: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑

Salt used: Calcium chloride (CaCl₂) is the salt formed in this process.
Marble chips (CaCO₃) react with dilute hydrochloric acid (HCl). CO₂ gas is collected by downward displacement of air in an erect gas jar (since CO₂ is denser than air).

1. Effective pest and disease control: Pesticides effectively kill or control insects, fungi, weeds, and other pests that destroy crops. Without them, crop losses due to pests would be enormous, threatening food security, especially in developing countries.

2. Increased crop yield and economic benefit: Pesticide use significantly increases agricultural productivity and ensures consistent crop yield. Farmers rely on them for economic reasons — without pesticides, they cannot compete in markets or sustain their livelihoods.

Mammal: Whale (ह्वेल) — Whales are marine mammals (Class Mammalia). Despite living in water, they breathe air through lungs, give birth to live young, nurse their young with milk, and are warm-blooded.

Least developed animal: Sea-horse (समुद्री घोडा) — Sea-horses are fish (Class Osteichthyes/Actinopterygii), which are among the least evolved vertebrates in the given list. Among all listed, fish (Osteichthyes) are evolutionarily more primitive compared to reptiles (crocodile, snake) and birds (peacock).

Given: m = 700 g = 0.7 kg, T₁ = 5°C, T₂ = 40°C, c (water) = 4200 J/kg°C

Formula: Q = mc∆T
∆T = 40 − 5 = 35°C
Q = 0.7 × 4200 × 35
Q = 0.7 × 147,000
Q = 1,02,900 J = 102.9 kJ

(i) Impure silver should be placed at A (Anode). In electrolytic refining, the impure metal is always the anode. Silver ions dissolve from the impure anode into the AgNO₃ solution, leaving impurities behind. Pure silver is deposited on the cathode (B).

(ii) C (Battery/Power source) provides the direct electric current (D.C.) that drives the electrolysis process. Without external electricity, electrolysis cannot occur. It maintains a potential difference that causes Ag⁺ ions to migrate from anode to cathode and deposit as pure silver.

Saturated hydrocarbon (alkane) with molecular mass 44 amu:
CₙH₂ₙ₊₂ → 12n + 2n + 2 = 44 → 14n = 42 → n = 3 → Propane (C₃H₈)

Structural formula of Propane:

H  H  H
|  |  |
H—C—C—C—H
|  |  |
H  H  H

Removing one H from each adjacent carbon (C1 and C2 or C2 and C3):
This forms a double bond between adjacent carbons → CH₂=CH–CH₃

IUPAC name: Propene (Prop-1-ene) — CH₂=CH–CH₃
It is an unsaturated hydrocarbon (alkene) with a double bond between C1 and C2.

s-Block Elements (Groups 1 & 2 — Alkali and Alkaline Earth Metals):
1. Their valence electrons are present in the s-subshell (1s or 2s). They have 1 or 2 valence electrons and form ions with +1 or +2 charge. Example: Na (2,8,1), Ca (2,8,8,2)
2. They are highly reactive metals with low ionisation energy and electronegativity. They react vigorously with water to form hydroxides and release hydrogen gas. They are good conductors of heat and electricity.

p-Block Elements (Groups 13–18):
1. Their valence electrons are in the p-subshell. They include metals, metalloids, and non-metals. Example: Al (2,8,3), Cl (2,8,7), Ne (2,8)
2. They show diverse properties — ranging from highly reactive non-metals (like F, Cl) to noble gases (He, Ne, Ar) that are almost completely inert. They form both covalent and ionic compounds with variable oxidation states.

(i) More growth of plant in sunlight:
• Independent variable: Amount/intensity of sunlight (the variable being changed or controlled)
• Dependent variable: Growth of plant (the variable being measured/observed — it depends on how much sunlight the plant receives)

(ii) Stretch of catapult and distance covered by stone:
• Independent variable: Stretch of the catapult (तन्काई — the experimenter controls how much the catapult is stretched)
• Dependent variable: Distance covered by the stone (the stone travels farther when the catapult is stretched more — this is what is measured)

Causes of Dispersion of Light:

1. White light is a mixture of seven colours of different wavelengths: White light is not a single colour but a mixture of VIBGYOR colours, each with a different wavelength. Violet has the shortest wavelength and red has the longest.

2. Different refractive indices for different colours: The refractive index of glass (or any dispersive medium) is different for different wavelengths/colours. Violet light has the highest refractive index in glass (bends the most), while red has the lowest (bends the least). This differential bending separates the colours.

Identification: Normal RBC = 4–6 million/mm³, WBC = 4,000–11,000/mm³, Platelets = 1,50,000–4,00,000/mm³
W = 30,00,000 = RBC (Red Blood Cells) · X = 3,000 = WBC (White Blood Cells) · Y = 3,50,000 = Platelets

(i) Y (Platelets — 3,50,000) is in normal condition. Normal platelet count = 1,50,000 to 4,00,000 per mm³. W (RBC) = 30,00,000 is low (normal = 40–60 lakh), X (WBC = 3,000) is low (normal = 4,000–11,000).

(ii) X = WBC = 3,000 (below normal 4,000). This condition is Leukopenia. The person has a weakened immune system — they become highly susceptible to infections (bacterial, viral, fungal) and cannot fight diseases effectively.

(iii) Y = Platelets dropping to 1,50,000 (borderline low). If it drops further or below normal, the person will suffer from Thrombocytopenia — the blood loses its ability to clot properly, causing excessive bleeding, easy bruising, and potentially dangerous internal bleeding. This condition is also seen in Dengue fever.

(iv) W (30,00,000 = 30 lakh — which is low normal range) is RBC (Red Blood Cells / Erythrocytes). They contain haemoglobin and are responsible for transporting oxygen from lungs to body tissues.

(i) Finding secondary turns:
Transformer ratio: Vₛ/Vₚ = Nₛ/Nₚ
480/240 = Nₛ/300
2 = Nₛ/300
Nₛ = 600 turns (Step-up transformer — secondary has more turns)

(ii) Lamination of transformer core:
The core is laminated (made of thin insulated sheets of soft iron) to reduce eddy currents. Eddy currents are induced currents that circulate within the iron core, generating heat and wasting energy. Lamination breaks these current paths, reducing energy loss and increasing transformer efficiency.

(iii) Transformer cannot be used in DC circuit.
Reason: A transformer works on the principle of electromagnetic induction, which requires a changing magnetic flux. DC (direct current) produces a constant (non-changing) magnetic field. Since there is no change in flux, no EMF is induced in the secondary coil. Therefore, a transformer does NOT work with DC.

This refers to Artificial Insemination (AI) — the technology of collecting semen from a superior male animal and mechanically introducing it into the uterus of a female.

(i) Two advantages:
1. Genetic improvement: Semen from a genetically superior male (high milk-producing bull, disease-resistant animal) can be used to inseminate thousands of females, rapidly improving the quality of livestock over generations.
2. Disease prevention and convenience: Direct contact between animals is not required, preventing transmission of sexually transmitted diseases. Semen can be stored (cryopreserved), transported, and used across long distances, saving time and cost.

(ii) Two points to be considered:
1. The female animal must be in the correct reproductive cycle (oestrus/heat phase) at the time of insemination to ensure successful fertilization.
2. Strict hygiene and sterilisation of all instruments must be maintained to prevent infection. The semen must be of high quality (checked for motility and viability) and stored at proper temperature (−196°C in liquid nitrogen for long-term storage).

Given: mₐ = 6×10²⁴ kg, m_b = 400 kg, R = 6400 km = 6.4×10⁶ m, G = 6.67×10⁻¹¹ Nm²/kg²

(i) Gravitational Force:
F = GmₐM_b / R²
F = (6.67×10⁻¹¹ × 6×10²⁴ × 400) / (6.4×10⁶)²
F = (6.67 × 6 × 400 × 10⁻¹¹⁺²⁴) / (40.96×10¹²)
F = (16,008 × 10¹³) / (40.96×10¹²)
F = 16,008/409.6 × 10
F ≈ 39.08 × 10 ≈ 3,910 N ≈ 3.92×10³ N
(This is approximately the weight of B on Earth: mg = 400×9.8 = 3920 N ✓)

(ii) Height for g = 6 m/s²:
g' = gR² / (R+h)²
At surface: g = 9.8 m/s² (or use g = GM/R²)
6 = 9.8 × R² / (R+h)²
(R+h)² = 9.8 R² / 6 = 1.633 R²
(R+h) = R√1.633 = R × 1.278
h = R(1.278 − 1) = 0.278 × R
h = 0.278 × 6400 km = ≈ 1,780 km