common-mistakes

target	495+/500
author	Senior Sibling
name	common-mistakes
description	Top 12th Grade Mistakes per Unit. Focus on Calculus precision, Organic mechanisms, Physics sign conventions, and Biotech terminology.

Common Mistakes Per Chapter — The 12th Grade "Mark-Killers"

📐 Mathematics

Integrals & Calculus

• ❌ The Constant of Integration ($+C$): Forgetting $+C$ in indefinite integrals. Examiners deduct 0.5m EVERY time.
• ❌ Property Labeling: Using the 'King Property' ($∫ f(a-x)$) without stating it.
• ❌ Differential Eq: Finding the wrong Integrating Factor ($e^{∫P dx}$) by misidentifying $P$.
• ❌ Limits: Evaluating $\int_a^b$ but substituting $a$ before $b$ (Upper - Lower!).

Vectors & 3D Geometry

• ❌ Shortest Distance: Forgetting the magnitude in the denominator $|\vec{b1} \times \vec{b2}|$.
• ❌ Dot vs Cross: Using $\cos \theta$ for cross product or $\sin \theta$ for dot product.
• ❌ Plane Equation: Forgetting that $n$ is the Normal vector, not a vector on the plane.

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🔭 Physics

Electrostatics & Current

• ❌ Units: Writing $10\mu C$ in a formula without converting to $10 \times 10^{-6} C$.
• ❌ Gauss Law: Forgetting the $2$ in the flux through a cylinder end-cap ($2EA$).
• ❌ Kirchhoff's: Wrong sign for $IR$ when moving against the current.

Optics (The Biggest Mark Leak)

• ❌ Sign Convention: Forgetting that $u$ is ALWAYS negative.
• ❌ Ray Diagrams: Drawing rays without ARROWS. Arrows are mandatory for 3-5 marks.
• ❌ Lens Maker: Using $n2 - n1$ but forgetting to divide by $n1$ (i.e., $(n2/n1 - 1)$).
• ❌ Power: Using $f$ in $cm$ in the formula $P = 1/f$. $f$ MUST be in meters.

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🧪 Chemistry

Organic Chemistry

• ❌ Aldol vs Cannizzaro: Attempting Aldol on an aldehyde with NO alpha-hydrogen (e.g., Benzaldehyde).
• ❌ Mechanism Arrows: Drawing arrows from positive to negative. Arrows ALWAYS show electron flow (negative $\to$ positive).
• ❌ Distinction Tests: Writing the observation without the reagent name.

Physical & Inorganic

• ❌ Nernst Equation: Using $\ln$ instead of $\log$ (or forgetting the $2.303$ factor).
• ❌ VBT: Identifying an octahedral complex as $sp^3d^2$ (outer) when it should be $d^2sp^3$ (inner).
• ❌ Kinetics: Using the Zero-order half-life formula for a First-order question.

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🧬 Biology

Genetics & Biotech

• ❌ Terminology: Confusing Translation (RNA to Protein) with Transcription (DNA to RNA).
• ❌ Lac Operon: Stating that Lactose is the "Repressor" (Lactose is the Inducer).
• ❌ PCR: Swapping the temperatures for Annealing and Extension.
• ❌ Pedigree: Confusing Autosomal Dominant with X-linked Recessive.

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💻 Computer Science

• ❌ Pickle Module: Using f.write() instead of pickle.dump(data, f) for binary files.
• ❌ SQL: Using WHERE after GROUP BY. You MUST use HAVING for groups.
• ❌ Indentation: Incorrect indentation in the Push/Pop stack logic.

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📖 English Core

• ❌ Job Application: Forgetting to attach the Bio-data/Resume after the cover letter.
• ❌ Notice: Writing the date in a confusing format (e.g., 10/12/26). Use "10th December 2026".
• ❌ Literature: Confusing the themes of "The Rattrap" (essential goodness) with "The Enemy" (humanity over war).