Arrhenius: Acid produces $H^+$, Base produces $OH^-$.
Brønsted-Lowry: Acid is $H^+$ donor, Base is $H^+$ acceptor.
Lewis: Acid is electron pair acceptor, Base is electron pair donor.

pH: $-\log[H^+]$. $pH + pOH = 14$ at $25^\circ C$.

Buffer Solution: Resists changes in pH upon addition of small amounts of acid or base (weak acid/conjugate base or weak base/conjugate acid).

Entropy ($\Delta S$): Measure of disorder or randomness in a system.

Enthalpy ($\Delta H$): Heat change at constant pressure. Exothermic ($\Delta H < 0$), Endothermic ($\Delta H > 0$).

4. Applied Chemistry

Food Preservation: Methods like lowering pH (vinegar), increasing sugar/salt concentration (hypertonicity), canning, refrigeration.
Vinegar: 6-10% acetic acid solution.
Antioxidants: Inhibit oxidation reactions that cause food spoilage and free radical formation.
Cleaning Agents:
- Soaps: Sodium/potassium salts of fatty acids. Form scum in hard water.
- Detergents: Synthetic cleaning agents, effective in hard water.
- Bleaching Powder: Calcium oxychloride ($CaOCl_2$).
Colloids: Mixtures with particle sizes between solutions and suspensions (1 nm - 1000 nm).
Emulsion: A colloid of two immiscible liquids (e.g., milk is fat in water).
Saponification: Hydrolysis of an ester (fat/oil) with a strong base to form soap and glycerol.

Part 1: 100 New Original Theoretical / Conceptual MCQs

Chapter 2: Qualitative Chemistry

Answer: Azimuthal (or angular momentum) quantum number ($l$).
- Concept: The azimuthal quantum number ($l$) defines the shape of an orbital (e.g., $l=0$ for $s$ (spherical), $l=1$ for $p$ (dumbbell), $l=2$ for $d$ (cloverleaf), $l=3$ for $f$ (complex)).
Answer: They must have opposite spins ($m_s$).
- Concept: Pauli Exclusion Principle states that no two electrons in the same atom can have identical values for all four quantum numbers. If they are in the same orbital, $n, l, m_l$ are the same, so $m_s$ must be different ($+1/2$ and $-1/2$).
Answer: $4s$ orbital has lower energy than $3d$ due to electron-electron repulsion and shielding effects (according to Aufbau principle).
- Concept: The Aufbau principle, combined with the $(n+l)$ rule, dictates the filling order. For $4s$, $n=4, l=0 \implies n+l=4$. For $3d$, $n=3, l=2 \implies n+l=5$. Lower $(n+l)$ means lower energy.
Answer: The electron absorbs energy.
- Concept: When an electron moves from a lower energy level ($n=2$) to a higher energy level ($n=4$), it must absorb energy corresponding to the energy difference between the two levels.
Answer: The nucleus must have a non-zero nuclear spin quantum number ($I \neq 0$).
- Concept: NMR (Nuclear Magnetic Resonance) spectroscopy relies on the magnetic properties of nuclei. Nuclei with an odd mass number or odd atomic number (and even mass number) have a non-zero spin and are NMR active (e.g., $^1H, ^{13}C, ^{31}P$).
Answer: Gamma rays.
- Concept: The electromagnetic spectrum ranges from low frequency (radio waves) to high frequency (gamma rays). Higher frequency corresponds to higher energy.
Answer: An orbit is a fixed,