Why?

1. m-OCH₃–phenol

• At meta, +M cannot operate
• Only –I → acidity increases
• Highest

2. Phenol

• Reference compound.

3. m-CH₃–phenol

• Meta CH₃ → mainly +I
• Acidity decreases slightly.

4. p-CH₃ and o-CH₃

• CH₃ has +I and hyperconjugation
• Both decrease acidity.
• o-CH₃ has additional steric/proximity effects, making it generally less acidic.

5. p-OCH₃ and o-OCH₃

• At o/p, +M of –OCH₃ operates strongly
• This destabilizes phenoxide → acidity decreases considerably.
• Ortho also has proximity/steric effects.

1. Lewis acid
   • Al has only 6 electrons around it in monomeric AlCl₃.
   • Therefore, AlCl₃ is an electron-deficient compound and acts as a Lewis acid.
2. Dimerisation
   • AlCl₃ exists as Al₂Cl₆ (especially in vapour/organic solvents under suitable conditions).Two AlCl₃ units are joined through two bridging Cl atoms.
   AlCl₃ ⇌ Al₂Cl₆
3. Hybridisation in AlCl₃
   • Monomeric AlCl₃ → sp², trigonal planar.
   • Al₂Cl₆ → each Al is approximately sp³ because of the two bridging Cl bonds

Most common JEE question

Q. The geometry and hybridisation of Al in monomeric AlCl₃ are:

A. Linear, sp
B. Trigonal planar, sp²
C. Tetrahedral, sp³
D. Pyramidal, sp³

Answer: B — Trigonal planar, sp².

Shortcut:
AlCl₃ = electron deficient → Lewis acid → dimerises to Al₂Cl₆.

so in di bridge structure two cordinate bonds

Yes. In the dimer Al₂​Cl₆​, there are two bridging Cl atoms, and the bonding is commonly represented with two coordinate (dative) bonds.

Al₂​Cl₆​​ structure

• Each AlCl₃ initially has 3 Al–Cl bonds.
• One Cl atom from each AlCl₃ donates a lone pair to the electron-deficient Al of the other unit.
• Thus, 2 bridging Cl atoms → 2 coordinate bonds.

Important: The two coordinate bonds are often drawn as Al←Cl. After formation, the Al–Cl bridging bonds can have considerable covalent character; the arrow mainly indicates the origin of the electron pair.

Here are NEET/JEE-ready notes from the given passage, with the most important facts highlighted.

Gynoecium — Female Reproductive Part

• Gynoecium = female reproductive part of a flower.
• It may be:
  • Monocarpellary → one pistil
  • Multicarpellary → more than one pistil
• Multicarpellary pistils may be:
  • Syncarpous → carpels fused
  • Apocarpous → carpels free

Parts of a Pistil

Stigma → Style → Ovary

Inside the ovary:

• Ovarian cavity = Locule
• Placenta is present inside the locule.
• Ovules (megasporangia) arise from the placenta.

Structure of Ovule

An ovule is attached to the placenta by a stalk called the funicle.

Important terms

Funicle → stalk attaching ovule to placenta
Hilum → junction between ovule and funicle
Integuments → protective coverings around nucellus
Micropyle → small opening in integuments
Chalaza → basal region opposite micropyle
Nucellus → mass of cells enclosed by integuments
Embryo sac → female gametophyte present inside nucellus

Simple arrangement

Micropyle → Nucellus + Embryo sac → Chalaza

Megasporogenesis

Megasporogenesis = formation of megaspores from Megaspore Mother Cell (MMC).

Sequence

Megaspore Mother Cell (MMC)
↓ Meiosis
4 megaspores
↓
1 functional megaspore + 3 degenerate

In most angiosperms:

Only ONE megaspore remains functional.

The development of embryo sac from a single functional megaspore is called:

Monosporic development

Ploidy — Very Important

Why does MMC undergo meiosis?

Because:

2n MMC → meiosis → four n megaspores

Thus, meiosis reduces chromosome number from diploid (2n) to haploid (n).

Formation of Embryo Sac

The functional megaspore undergoes three successive mitotic divisions.

Nuclear stages:

1 nucleus
↓ mitosis
2 nuclei
↓ mitosis
4 nuclei
↓ mitosis
8 nuclei

These divisions are free-nuclear divisions because:

Nuclear division occurs without immediate cell-wall formation.

After the 8-nucleate stage, cell walls are formed.

Mature Embryo Sac

A typical angiosperm embryo sac is:

8-nucleate but 7-celled

This is one of the most important NEET facts.

Arrangement

Micropylar end:

• 2 Synergids
• 1 Egg

Together = Egg apparatus

Chalazal end:

• 3 Antipodals

Central cell:

• 2 Polar nuclei

Therefore:

3 cells + 3 cells + 1 central cell = 7 cells

But nuclei:

3 + 3 + 2 polar nuclei = 8 nuclei

Hence:

Embryo sac = 7-celled and 8-nucleate

Egg Apparatus

The egg apparatus consists of:

2 Synergids + 1 Egg cell

Synergids have:

Filiform apparatus

Function:

Guides the pollen tube into the synergid.

One-Line NEET Revision

Gynoecium → Pistil → Stigma + Style + Ovary

Ovary → Locule → Placenta → Ovules

Ovule → Funicle + Hilum + Integuments + Micropyle + Nucellus + Embryo sac

MMC (2n) → meiosis → 4 megaspores (n) → 1 functional megaspore → 3 mitotic divisions → 8 nuclei → 7-celled, 8-nucleate embryo sac

Embryo sac formula:

Micropylar: 2 Synergids + 1 Egg
Central: 2 Polar nuclei
Chalazal: 3 Antipodals

Total = 7 cells + 8 nuclei 🌟

Step 1: Identify the optically active alkyl bromide (A)

Given molecular formula = C₄H₉Br and it is optically active.

Possible isomers:

• CH₃CH₂CH₂CH₂Br (1-bromobutane) ❌
• CH₃CHBrCH₂CH₃ (2-bromobutane) ✅ (chiral)
• (CH₃)₂CHCH₂Br (isobutyl bromide) ❌
• (CH₃)₃CBr (tert-butyl bromide) ❌

Hence,A=2-bromobutane​

Step 2: Alcoholic KOH (Hot)

Step 3: Addition of Br₂

​

Step 4: Reaction with alcoholic NaNH₂

Vicinal dibromide + excess NaNH₂ undergoes double dehydrohalogenation.

Step 5: Hydration of alkyne

Conditions:

• HgSO₄
• Dil. H₂SO₄
• 333 K

Hydration of an internal alkyne gives a ketone after keto-enol tautomerism.

Final Answer

(3) Butan-2-one​

​​​

1. Atomic Theory Gets Experimental Support

• By the 19th century, many experiments supported the atomic theory of matter.
• Scientists became convinced that all matter is made up of atoms.

2. Discovery of Electron (1897) – J. J. Thomson

J. J. Thomson performed experiments on electric discharge through gases.

Observations:

• Atoms contain negatively charged particles called electrons.
• Electrons are identical in all elements.
• Since atoms are electrically neutral, there must also be positive charge inside the atom.

3. Thomson’s Atomic Model (1898)

J. J. Thomson proposed the first atomic model.

Main Features

• Positive charge is uniformly spread throughout the atom.
• Electrons are embedded in the positive sphere.
• Similar to:
  • Plum pudding
  • Watermelon with seeds

Limitation

• Later experiments proved this model incorrect.

Continuous Spectrum vs Line Spectrum

A. Continuous Spectrum

Produced by:

• Solids
• Liquids
• Dense gases

Characteristics

• Contains all wavelengths.
• Intensity varies with wavelength.
• Caused by interaction among neighbouring atoms and molecules.

Examples

• Hot iron
• Sunlight
• Incandescent bulb

B. Line Spectrum

Produced by:

• Rarefied gases
• Electrically excited gases

Examples

• Neon sign
• Mercury vapour lamp
• Hydrogen discharge tube

Characteristics

• Contains only certain discrete wavelengths.
• Appears as bright coloured lines.
• Produced by individual atoms.

Characteristic Spectrum of Elements

Every element has its own unique spectrum.

For example:

• Hydrogen always produces the same set of spectral lines.
• No two elements have identical spectra.

Importance

This suggested that:

• Every atom has a unique internal structure.
• Spectrum depends on the arrangement of particles inside the atom.

Balmer’s Contribution (1885)

Johann Jakob Balmer gave an empirical formula for the wavelengths of visible lines in the hydrogen spectrum.

Importance

• First successful mathematical relation for atomic spectra.
• Helped later scientists develop atomic models.

Rutherford’s Alpha Scattering Experiment

Ernest Rutherford studied α-particles emitted by radioactive substances.

Experiment Proposed

• Proposed in 1906
• Performed around 1911 by:
  • Hans Geiger
  • Ernest Marsden

Objective

To determine the internal structure of the atom.

Rutherford’s Nuclear (Planetary) Model

Main Features

• Almost all positive charge is concentrated in a tiny nucleus.
• Nearly all the mass is inside the nucleus.
• Electrons revolve around the nucleus like planets around the Sun.
• Most of the atom is empty space.

Limitation of Rutherford’s Model

It could not explain:

• Why atoms emit only specific wavelengths.
• Why hydrogen gives a line spectrum instead of a continuous spectrum.
• Why revolving electrons do not lose energy and fall into the nucleus (according to classical physics).

These problems led to the development of Bohr’s atomic model.

Important Years

JEE/NEET One-Liners

• Atom is electrically neutral.
• Electron was discovered by J. J. Thomson (1897).
• Thomson’s model is called the Plum Pudding Model.
• Continuous spectrum contains all wavelengths.
• Line spectrum contains discrete wavelengths.
• Every element has a characteristic spectrum.
• Balmer gave the formula for the visible hydrogen spectrum.
• Rutherford’s experiment used α-particles.
• Positive charge is concentrated in the nucleus.
• Rutherford’s model failed to explain the line spectrum and atomic stability.

Memory Trick

T → B → R → B

• T = Thomson discovers electron
• B = Balmer explains hydrogen spectrum
• R = Rutherford discovers nucleus
• B = Bohr explains line spectrum & atomic stability

1. Concept of Health

Ancient Concept of Health

• Early Greeks (e.g., Hippocrates) and the Ayurveda system believed health depended on the balance of four “humors”.
• One humor was black bile.
• They believed people with excess black bile had a hot personality and suffered from fever.
• This was based on observation and philosophical thinking, not experiments.

Modern Scientific Concept

• William Harvey discovered blood circulation through experiments.
• The invention of the thermometer proved that people with black bile did not necessarily have higher body temperature.
• Thus, the humor theory was disproved.

Modern Definition of Health (WHO)

Health is a state of complete physical, mental, and social well-being, and not merely the absence of disease or physical fitness.

Three Components of Health

1. Physical Health

• Proper functioning of body organs
• Freedom from illness
• Good physical fitness

2. Mental Health

• Ability to think clearly
• Emotional stability
• Freedom from stress and anxiety

3. Social Health

• Good relationships
• Ability to work with others
• Positive participation in society

Factors Affecting Health

1. Genetic Disorders

Defects present from birth due to inheritance from parents.

Examples

• Haemophilia
• Sickle-cell anaemia
• Colour blindness

2. Infections

Diseases caused by microorganisms like:

• Bacteria
• Viruses
• Fungi
• Protozoa
• Helminths (worms)

3. Lifestyle Factors

• Balanced diet
• Safe drinking water
• Proper rest
• Regular exercise
• Personal hygiene
• Avoiding smoking, alcohol and drugs

Role of Mind in Health

Modern biology explains that:

Mind → Nervous System + Endocrine System → Immune System → Health

• Mental stress weakens immunity.
• Positive mental health improves resistance to disease.

Importance of Good Health

Good health leads to:

• Higher work efficiency
• Increased productivity
• Economic prosperity
• Longer lifespan (longevity)
• Lower infant mortality
• Lower maternal mortality
• Better quality of life

Measures to Maintain Good Health

• Balanced diet
• Personal hygiene
• Regular exercise
• Yoga
• Vaccination (Immunisation)
• Awareness about diseases
• Safe drinking water
• Hygienic food
• Proper waste disposal
• Control of disease vectors (mosquitoes, flies, etc.)

Yoga

Benefits:

• Improves physical fitness
• Reduces stress
• Enhances mental health
• Improves flexibility
• Strengthens immunity

Disease

Definition

A disease is a condition in which the normal functioning of one or more organs or body systems is disturbed, producing characteristic signs and symptoms.

Signs vs Symptoms

Classification of Diseases

1. Infectious (Communicable) Diseases

Definition

Diseases that spread from one person to another through pathogens.

Characteristics

• Caused by microorganisms
• Communicable
• Preventable by hygiene and vaccination

Examples

• Tuberculosis (TB)
• Malaria
• Typhoid
• Cholera
• Measles
• Chickenpox
• Influenza
• COVID-19
• AIDS

Important Point

Some infectious diseases like AIDS are fatal.

2. Non-Infectious (Non-Communicable) Diseases

Definition

Diseases that do not spread from one person to another.

Causes

• Genetic defects
• Nutritional deficiency
• Hormonal imbalance
• Lifestyle
• Ageing
• Cancer

Examples

• Diabetes
• Hypertension
• Cancer
• Heart disease
• Asthma
• Haemophilia

Important Point

Among non-infectious diseases, cancer is a major cause of death.

Drug and Alcohol Abuse

Drug and alcohol abuse:

• Damages the brain
• Affects liver and heart
• Weakens immunity
• Reduces work efficiency
• May lead to addiction and mental disorders

NEET Important Flow Chart

Health
│
├── Physical Well-being
├── Mental Well-being
└── Social Well-being
        │
        ▼
Factors Affecting Health
│
├── Genetic Disorders
├── Infections
└── Lifestyle
        │
        ▼
Good Health
│
├── Balanced Diet
├── Hygiene
├── Exercise
├── Yoga
├── Vaccination
├── Waste Disposal
└── Vector Control
        │
        ▼
Disease
│
├── Infectious
│     ├── Communicable
│     └── Example: TB, Malaria, AIDS
│
└── Non-Infectious
      ├── Non-communicable
      └── Example: Cancer, Diabetes

NCERT & NEET Important Points

• Health is not merely the absence of disease.
• Health includes physical, mental, and social well-being.
• Mind influences health through the nervous system, endocrine system, and immune system.
• Health is affected by genetic disorders, infections, and lifestyle.
• Balanced diet, hygiene, exercise, yoga, vaccination, waste disposal, and vector control help maintain health.
• Infectious diseases are communicable.
• Non-infectious diseases are non-communicable.
• Cancer is a major non-infectious disease.
• AIDS is an infectious and fatal disease.

One-Line Revision

• Health = Physical + Mental + Social well-being
• Disease = Disturbed body function
• Infectious = Communicable
• Non-infectious = Non-communicable
• Good health → Higher productivity + Longer life
• Balanced diet + Hygiene + Exercise + Vaccination = Healthy life

What is Life History?

Life history refers to the pattern of growth, reproduction, and survival of an organism throughout its life.

It includes traits such as:

• Age at first reproduction
• Number of times an organism reproduces
• Number of offspring produced
• Size of offspring
• Lifespan

Main Idea

• Every population evolves to maximize its reproductive fitness (Darwinian fitness).
• Darwinian fitness means the ability of an organism to leave the maximum number of surviving offspring in the next generation.
• Organisms evolve the most suitable reproductive strategy according to their habitat and environmental conditions.