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Top 30 “Must-Do” Lewis Structures for JEE/NEET

Master List of Important Lewis Structure Compounds for JEE/NEET

1. Octet Rule Molecules

H₂

N₂

O₂

F₂

Cl₂

Br₂

I₂

HF

HCl

HBr

HI

H₂O

H₂S

NH₃

PH₃

CH₄

SiH₄

CO₂

CS₂



—

2. Electron-Deficient Compounds

BeH₂

BeCl₂

BH₃

BF₃

BCl₃

AlCl₃



—

3. Odd-Electron Molecules

NO

NO₂

ClO₂

BrO₂

IO₂

O₂⁻

N₃ (azide radical, less common)



—

4. Resonance Species

O₃

CO₃²⁻

NO₂⁻

NO₃⁻

SO₂

SO₃

IO₃⁻

BrO₃⁻

ClO₃⁻

CN⁻

N₃⁻

HN₃



—

5. Polyatomic Ions

NH₄⁺

H₃O⁺

OH⁻

CN⁻

NO₂⁻

NO₃⁻

CO₃²⁻

HCO₃⁻

SO₃²⁻

SO₄²⁻

HSO₄⁻

PO₄³⁻

HPO₄²⁻

H₂PO₄⁻

ClO⁻

ClO₂⁻

ClO₃⁻

ClO₄⁻

BrO⁻

BrO₂⁻

BrO₃⁻

BrO₄⁻

IO⁻

IO₂⁻

IO₃⁻

IO₄⁻

I₃⁻

S₄O₆²⁻

S₂O₃²⁻



—

6. Hypervalent (Expanded Octet) Molecules

PCl₅

PF₅

SF₄

SF₆

ClF₃

BrF₃

IF₃

IF₅

IF₇

XeF₂

XeF₄

XeF₆

ICl₃



—

7. Xenon Compounds

XeF₂

XeF₄

XeF₆

XeO₃

XeO₄



—

8. Peroxides and Superoxides

H₂O₂

Li₂O₂

Na₂O₂

K₂O₂

MgO₂

CaO₂

SrO₂

BaO₂

KO₂

RbO₂

CsO₂



—

9. Peroxo Acids of N, P, S

HNO₄

ONOO⁻

H₃PO₅

H₄P₂O₈

H₂SO₅ (Caro’s acid)

H₂S₂O₈ (Marshall’s acid)



—

10. Sulfur Oxyanions

SO₃²⁻

SO₄²⁻

S₂O₃²⁻ (Thiosulfate)

S₄O₆²⁻ (Tetrathionate)

HSO₄⁻



—

11. Nitrogen Special Compounds

NO

NO₂

N₂O

N₂O₃

N₂O₄

N₂O₅

HN₃

N₃⁻



—

12. Carbon Special Compounds

CO

CO₂

C₃O₂ (Carbon suboxide)

CN⁻



—

13. Bromine–Oxygen Compounds

Br₂O

Br₂O₃

Br₂O₅

Br₂O₇

Br₃O₈

HBrO

HBrO₂

HBrO₃

HBrO₄

BrO⁻

BrO₂⁻

BrO₃⁻

BrO₄⁻



—

14. Iodine Compounds

IF₃

IF₅

IF₇

ICl₃

I₃⁻

HIO

HIO₂

HIO₃

HIO₄

H₅IO₆

IO⁻

IO₂⁻

IO₃⁻

IO₄⁻

I₂O

I₂O₃

I₂O₅

I₂O₇



—

Top 30 “Must-Do” Lewis Structures for JEE/NEET

NH₄⁺, H₃O⁺, BF₃, BeCl₂, CO, NO, NO₂, O₃, NO₂⁻, NO₃⁻, CO₃²⁻, SO₂, SO₃, SO₄²⁻, CN⁻, N₃⁻, HN₃, PCl₅, SF₄, SF₆, ClF₃, IF₃, IF₅, IF₇, XeF₂, XeF₄, XeF₆, I₃⁻, S₂O₃²⁻, S₄O₆²⁻.

If you can draw and analyze these 30 confidently (Lewis structure, formal charge, hybridisation, shape, bond angle, resonance), you’ll cover nearly all Lewis-structure-based questions in JEE and NEET.

Formation of Embryo Sac (Polygonum Type) Reproduction class 12

  1. The functional megaspore enlarges and develops into the embryo sac.
  2. The nucleus of the functional megaspore undergoes mitotic division to form 2 nuclei.
  3. These two nuclei move to opposite poles, forming the 2-nucleate embryo sac.
  4. The nuclei divide again mitotically to form the 4-nucleate stage.
  5. A third mitotic division produces the 8-nucleate stage.
  6. These divisions are free-nuclear divisions, meaning:
    • Nuclear division occurs.
    • Cell wall formation does not occur immediately.
  7. After the 8-nucleate stage, cell walls are formed, organizing the embryo sac.
  8. Out of the 8 nuclei:
    • 6 nuclei are enclosed by cell walls to form cells.
    • 2 nuclei remain free in the central cell as polar nuclei.

Arrangement of Cells in Mature Embryo Sac

Micropylar End (Egg Apparatus)

  1. Three cells are present at the micropylar end, called the egg apparatus:
    • 1 Egg cell
    • 2 Synergids
  2. Synergids possess filiform apparatus (finger-like wall thickenings) which:
    • Guide the pollen tube into the embryo sac.
    • Help in nutrient transfer.

Chalazal End

  1. Three cells are present at the chalazal end called antipodal cells.

Central Cell

  1. The large central cell contains two polar nuclei.

Mature Embryo Sac Summary

  • Total nuclei = 8
  • Total cells = 7
    • 1 Egg cell
    • 2 Synergids
    • 3 Antipodal cells
    • 1 Central cell (with 2 polar nuclei)

Concave Mirror: All Possible Image Formations class 12 cbse

Concave Mirror: All Possible Image Formations

Object PositionImage PositionNature of ImageSize
At infinityAt FReal, invertedHighly diminished (point-sized)
Beyond CBetween C and FReal, invertedDiminished
At CAt CReal, invertedSame size
Between C and FBeyond CReal, invertedEnlarged
At FAt infinityReal, invertedHighly enlarged
Between F and PBehind mirrorVirtual, erectEnlarged

Key:

  • P = Pole
  • F = Principal Focus
  • C = Centre of Curvature

Convex Mirror: All Possible Image Formations

Object PositionImage PositionNature of ImageSize
At infinityAt F (behind mirror)Virtual, erectHighly diminished
Anywhere in front of mirrorBetween P and F (behind mirror)Virtual, erectDiminished

Quick NEET/JEE Points

  1. Concave mirror can form both real and virtual images.
  2. Convex mirror always forms virtual, erect, and diminished images.
  3. Real images are inverted and can be obtained on a screen.
  4. Virtual images cannot be obtained on a screen.
  5. Convex mirrors are used as rear-view mirrors because they provide a wider field of view.

Health and Disease – Important Points Class 12 Biology

Health and Disease – Important Points

Meaning of Health

  • Earlier, health was considered a balance of certain “humors” in the body.
  • Ancient Greek physician Hippocrates and the Indian Ayurveda system supported this idea.
  • People believed that excess “black bile” caused fever and hot personality.

Scientific Development of Health Concept

  • William Harvey discovered blood circulation using experimental methods.
  • Thermometer studies showed that people with “black bile” had normal body temperature.
  • This disproved the old “good humor” theory.

Modern Definition of Health

Health is a state of:

  1. Physical well-being
  2. Mental well-being
  3. Social well-being

Health does not mean only absence of disease or physical fitness.

Importance of Good Health

  • Increases working efficiency
  • Improves productivity
  • Brings economic prosperity
  • Increases life span (longevity)
  • Reduces infant mortality
  • Reduces maternal mortality

Ways to Maintain Good Health

  • Balanced diet
  • Personal hygiene
  • Regular exercise
  • Practice of yoga
  • Awareness about diseases
  • Vaccination (immunisation)
  • Proper disposal of wastes
  • Control of disease vectors
  • Clean food and water

Disease

  • When one or more organs or body systems do not function properly, disease occurs.
  • Disease is identified by various signs and symptoms.

Types of Diseases

1. Infectious Diseases

  • Spread from one person to another.
  • Caused by pathogens.
  • Common examples:
    • Cold
    • Flu
    • AIDS

2. Non-infectious Diseases

  • Do not spread from person to person.
  • Examples:
    • Cancer
    • Diabetes

Harmful Effects of Drug and Alcohol Abuse

  • Damage physical and mental health
  • Reduce body efficiency
  • Affect nervous system and organs

Factors Affecting Health

Health is affected by:

(i) Genetic Disorders

  • Defects inherited from parents
  • Disorders present from birth

(ii) Infections

  • Diseases caused by microorganisms

(iii) Lifestyle

  • Food and water intake
  • Rest and exercise
  • Personal habits

Role of Mind and Immune System

  • Mind influences the nervous system and endocrine system.
  • These systems affect the immune system.
  • A healthy mental state helps maintain good health.

Experimental Arrangement for Study of Photoelectric Effect

Experimental Arrangement for Study of Photoelectric Effect

Figure 11.1 shows the experimental setup used to study the photoelectric effect. The arrangement consists of an evacuated glass or quartz tube containing two metal plates:

  • Plate C → Photosensitive plate (Emitter)
  • Plate A → Collector plate

A source of monochromatic light (S) sends light through a quartz window (W) onto the photosensitive plate (C).

Why is a quartz window used?

Quartz allows ultraviolet rays to pass through it, unlike ordinary glass. Since ultraviolet light is often needed to produce photoelectric emission, a quartz window is used.

Working of the Experiment

When light of sufficiently high frequency falls on the photosensitive plate (C):

  • Electrons are emitted from the surface of plate (C).
  • These emitted electrons are called photoelectrons.

A battery is connected between plates (A) and (C), creating an electric field.

  • If collector plate (A) is kept positive with respect to emitter plate (C), the emitted electrons are attracted towards plate (A).
  • Due to the movement of electrons, an electric current flows in the circuit. This current is called photoelectric current.

Measuring Instruments Used

  • Voltmeter (V): Measures the potential difference between plates (A) and (C).
  • Microammeter ((\mu A)): Measures the small photoelectric current flowing in the circuit.

Role of the Battery and Commutator

The battery maintains a variable potential difference between the two plates.

Using a commutator, the polarity of the plates can be reversed:

  • Plate (A) can be made positive or negative with respect to plate (C).
  • By changing the potential difference, the photoelectric current can be increased or decreased.

What Can Be Studied Using This Setup?

Using this arrangement, we can study how photocurrent depends on:

  1. Intensity of incident light
  2. Frequency of incident light
  3. Potential difference between plates (A) and (C)
  4. Nature of the photosensitive material

How Are Intensity and Frequency Varied?

(i) Changing Frequency

Different frequencies of light are obtained by using:

  • Coloured filters
  • Coloured glass plates

(ii) Changing Intensity

The intensity of light is changed by:

  • Varying the distance between the light source and the emitter plate

Important Point

Photoelectric emission occurs only when the incident light has frequency greater than a certain minimum value called the threshold frequency of the material.

Exponential Population Growth class 12 ecology

Facts from the Page (Exponential Population Growth)

  • Population growth can occur when resources like food and space are unlimited.
  • Under ideal conditions, population shows exponential growth.
  • The increase depends on:
    • Birth rate (b)
    • Death rate (d)

Example values of rrr:

  • Norway rat → 0.015
  • Flour beetle → 0.12
  • Human population → 0.16

Any species can grow exponentially for some time if resources are unlimited. Exponential growth produces a J-shaped curve. In the graph:

  • KKrepresents carrying capacity.

Population cannot grow indefinitely in nature because environmental resistance and limited resources act as checks.

Facts from the “King and Wheat” Story

  • A king offered a reward to a wise man.
  • The wise man asked for wheat grains on a chessboard:
    • 1 grain on first square
    • 2 on second
    • 4 on third
    • doubling on every next square
  • Total squares on chessboard = 64.
  • The number of grains increased enormously.
  • The king’s entire kingdom could not supply so much wheat.
  • This story demonstrates:
    • Exponential increase
    • Population can grow rapidly under unlimited conditions
    • Resources eventually become insufficient

Nutrition in Human Beings – Important Facts class 10 C

  • The digestive system consists of the alimentary canal extending from mouth to anus.
  • Different parts of the alimentary canal are specialised for different functions.
  • Food is broken into small particles for easy digestion and absorption.

Mouth and Buccal Cavity

  • Teeth crush and grind food.
  • Saliva is secreted by salivary glands.
  • Saliva contains the enzyme salivary amylase.
  • Salivary amylase converts starch into simple sugars.
  • The tongue mixes food with saliva and helps in swallowing.
  • Food becomes soft and moist for smooth passage.

Oesophagus and Peristalsis

  • Food passes from mouth to stomach through the oesophagus (food pipe).
  • Rhythmic contraction and relaxation of muscles push food forward.
  • These movements are called peristaltic movements.

Stomach

  • The stomach is a muscular expandable organ.
  • Gastric glands in the stomach wall secrete:
    • Hydrochloric acid (HCl)
    • Pepsin (protein-digesting enzyme)
    • Mucus
  • HCl creates an acidic medium for pepsin action.
  • HCl also kills harmful germs present in food.
  • Mucus protects the stomach lining from acid.
  • Food is released slowly into the small intestine through a sphincter muscle.

Small Intestine

  • The small intestine is the longest part of the alimentary canal.
  • Complete digestion of carbohydrates, proteins, and fats occurs here.
  • Herbivores have longer small intestines than carnivores.

Role of Liver

  • The liver secretes bile juice.
  • Bile:
    • Makes acidic food alkaline.
    • Breaks large fat globules into smaller droplets (emulsification).

Role of Pancreas

  • The pancreas secretes pancreatic juice.
  • Pancreatic enzymes include:
    • Trypsin → digests proteins.
    • Lipase → digests fats.

Intestinal Juice

  • Intestinal glands secrete intestinal juice.
  • Final digestion converts:
    • Proteins → amino acids
    • Carbohydrates → glucose
    • Fats → fatty acids and glycerol

Absorption

  • The inner lining of the small intestine has finger-like projections called villi.
  • Villi increase surface area for absorption.
  • Villi contain many blood vessels.
  • Absorbed nutrients are transported to all body cells.

Large Intestine and Egestion

  • Undigested food enters the large intestine.
  • Water is absorbed from the remaining material.
  • Waste is removed through the anus.
  • The anal sphincter controls the exit of waste.

Facts – Nutrition in Unicellular Organisms class 10th CBSE

  • Different organisms have different digestive systems because:
    • Their food differs.
    • Their method of obtaining food differs.
  • In simple unicellular organisms, food is taken in through the entire body surface.
  • As organisms become more complex, different body parts become specialised for digestion.

Amoeba

  • Amoeba uses temporary finger-like projections called pseudopodia to capture food.
  • The pseudopodia surround the food particle and form a food vacuole.
  • Inside the food vacuole:
    • Complex food substances are broken into simpler substances.
    • Digested food diffuses into the cytoplasm.
  • Undigested food is moved to the cell surface and expelled outside.

Paramoecium

  • Paramecium has a fixed body shape.
  • Food enters through a specific spot in the body.
  • Tiny hair-like structures called cilia help in feeding.
  • Movement of cilia pushes food towards the food intake region.

The Pistil, Megasporangium (ovule) and Embryo sac Class 12

Facts about Gynoecium, Ovule and Embryo Sac

Gynoecium

  1. Gynoecium is the female reproductive part of a flower.
  2. It may consist of:
    • One pistil → Monocarpellary
    • More than one pistil → Multicarpellary
  3. Multicarpellary pistils may be:
    • Fused together → Syncarpous
    • Free from each other → Apocarpous
  4. Each pistil has three parts:
    • Stigma – receives pollen grains
    • Style – slender stalk below stigma
    • Ovary – swollen basal part
  5. Inside the ovary is the ovarian cavity (locule).
  6. Placenta is present inside the ovary and bears ovules.

Ovule (Megasporangium)

  1. Ovules arise from the placenta.
  2. Ovules are also called megasporangia.
  3. Number of ovules may vary:
    • One ovule → wheat, paddy, mango
    • Many ovules → papaya, watermelon, orchids
  4. Ovule is attached to placenta by a stalk called funicle.
  5. The point where funicle joins ovule is called hilum.
  6. Ovule has one or two protective layers called integuments.
  7. Integuments leave a small opening called micropyle.
  8. The opposite end of micropyle is called chalaza.
  9. The central tissue inside ovule is called nucellus.
  10. Nucellus stores reserve food material.
  11. Female gametophyte or embryo sac is present inside nucellus.
  12. Usually one embryo sac develops from one megaspore.

Megasporogenesis

  1. Formation of megaspores from megaspore mother cell is called megasporogenesis.
  2. Megaspore mother cell undergoes meiosis to form megaspores.
  3. Usually four megaspores are produced.
  4. Generally only one megaspore remains functional.

Embryo Sac Development

  1. Functional megaspore develops into embryo sac.
  2. Nucleus divides mitotically to form:
  • 2-nucleate stage
  • 4-nucleate stage
  • 8-nucleate stage
  1. Initial nuclear divisions are free nuclear divisions (without cell wall formation).
  2. Later cell walls form and organise the embryo sac.
  3. Typical angiosperm embryo sac is:
  • 8-nucleate
  • 7-celled

Structure of Embryo Sac

  1. Three cells at micropylar end form the egg apparatus.
  2. Egg apparatus consists of:
  • One egg cell
  • Two synergids
  1. Synergids possess filiform apparatus.
  2. Filiform apparatus helps guide pollen tube.
  3. Three cells at chalazal end are called antipodals.
  4. Central cell contains two polar nuclei.
  5. Polar nuclei later participate in double fertilisation.

Important Terms

  1. Micropyle → opening for pollen tube entry
  2. Chalaza → basal region of ovule
  3. Hilum → junction of ovule and funicle
  4. Funicle → stalk attaching ovule to placenta
  5. Nucellus → nutritive tissue of ovule
  6. Embryo sac → female gametophyte of angiosperms

Important Structures from “The Pistil, Megasporangium (Ovule) and Embryo Sac”

(Class 12 Biology – CBSE Boards)

1. Structure of Pistil (Most Basic Diagram)

Important Labels

  • Stigma
  • Style
  • Ovary
  • Ovule

Important Terms

  • Monocarpellary
  • Multicarpellary
  • Syncarpous
  • Apocarpous

Board Questions

  • Draw labelled diagram of pistil.
  • Differentiate syncarpous and apocarpous.

2. Structure of Ovule (VERY IMPORTANT)

Most Important Labels

  • Funicle
  • Hilum
  • Micropyle
  • Chalaza
  • Integuments
  • Nucellus
  • Embryo sac

Must Learn Definitions

  • Funicle → stalk attaching ovule to placenta
  • Hilum → junction of ovule and funicle
  • Micropyle → opening in integuments
  • Chalaza → basal end opposite micropyle
  • Nucellus → nutritive tissue

Frequently Asked

  • Draw labelled diagram of anatropous ovule.
  • What is micropyle/hilum/chalaza?

3. Megasporogenesis

Important Points

  • Megaspore mother cell undergoes meiosis.
  • Four megaspores formed.
  • Usually one functional megaspore survives.

Important Terms

  • MMC (Megaspore Mother Cell)
  • Functional megaspore

Board Questions

  • Define megasporogenesis.
  • Why is embryo sac monosporic?

4. Structure of Embryo Sac (MOST IMPORTANT)

Must Learn Labels

  • Egg cell
  • Synergids
  • Filiform apparatus
  • Polar nuclei
  • Central cell
  • Antipodals
  • Micropylar end
  • Chalazal end

Key Facts

  • Embryo sac is:
    • 7-celled
    • 8-nucleate
  • Egg apparatus consists of:
    • 1 egg cell
    • 2 synergids
  • Central cell contains 2 polar nuclei.
  • Antipodals present at chalazal end.

Most Important Board Questions

  • Draw labelled diagram of mature embryo sac.
  • Explain 7-celled 8-nucleate condition.
  • What is filiform apparatus?

Most Important Structures to Memorise for Boards

StructureImportance
PistilBasic
OvuleVery Important
MegasporogenesisImportant Process
Embryo SacMOST IMPORTANT

One-Line Revision

  • Micropyle → pollen tube entry
  • Hilum → ovule-funicle junction
  • Nucellus → food tissue
  • Synergids → guide pollen tube
  • Antipodals → chalazal cells
  • Polar nuclei → triple fusion
  • Embryo sac → female gametophyte