By SenaPrep Defence Team Updated July 2026 9 min read
Cracking the UPSC National Defence Academy (NDA) written examination requires a highly focused preparation timeline. In this comprehensive study guide, our defence education experts analyze the core concepts of acids bases salts GAT, pH scale notes NDA, chemical indicators properties, outline high-yield preparation tips, and provide step-by-step examples.
Part 1: Chemical Properties of Acids, Bases and Salts
Chemistry in GAT General Science is mostly based on CBSE Class 9 and 10 concepts. Memorize these important definitions and formulas:
Bronsted-Lowry Theory: Acids are proton donors; Bases are proton acceptors.
Lewis Theory: Acids are electron-pair acceptors; Bases are electron-pair donors.
Chemical Formulas of Common Salts
Common Name
Chemical Name
Formula
Baking Soda
Sodium Bicarbonate
$NaHCO_3$
Washing Soda
Sodium Carbonate Decahydrate
$Na_2CO_3 \cdot 10H_2O$
Plaster of Paris
Calcium Sulphate Hemihydrate
$CaSO_4 \cdot \frac{1}{2}H_2O$
Bleaching Powder
Calcium Oxychloride
$CaOCl_2$
Syllabus Breakdown & Marks Allocation
Subject Segment
Total Questions
Weightage (Marks)
Preparation Priority
Paper 1: Mathematics
120 Questions
300 Marks
Critical (Sectional Cutoff)
Paper 2: GAT (English)
50 Questions
200 Marks
High Yield (4 Marks/Q)
Paper 2: GAT (General Knowledge)
100 Questions
400 Marks
High Scoring (Science & GS)
Part 2: Key Revision Strategies for acids bases salts GAT, pH scale notes NDA, chemical indicators properties
Success in this topic requires consistent daily practice. Here are the core routines recommended by top defence educators:
Build Foundational Concepts: Rely on Class 11 and 12 NCERT books for math/science topics, and read standard grammar texts for English.
Solve Previous Year Papers (PYQs): Go through at least the last 5-10 years of UPSC question sets to analyze repeat question structures.
Speed & Time Management: Practice mock tests with a timer to improve your answering speed. You have only 75 seconds per math question in the real exam.
Track Weak Areas: Bookmark difficult problems and review your mistake history to continuously raise your score.
Part 3: Practical Questions & Solved Examples
Below is a preview of the type of questions asked by the UPSC. Test your current understanding of acids bases salts GAT, pH scale notes NDA, chemical indicators properties and review the step-by-step methods:
Use the interactive test panel below to solve live questions pulled directly from the SenaPrep exam bank.
Interactive Practice Quiz
Test your preparation live! Choose an option for each question to see instant feedback and deep step-by-step explanations.
Question 1 of 5 Live App Practice
Which one of the following solutions is not capable of conducting electricity?
Detailed Solution:
Correct Answer
✓ Option (C) is correct. Sugar solution does not conduct electricity.
📖 Governing Law / Core Concept
A substance can only conduct electricity if it contains charged particles (ions) that are free to move. This is governed by the concept of electrolytic conduction.
🧪 Step-by-Step Breakdown
Sugar (C12H22O11) is a covalent compound. In aqueous solution, it dissolves but does not dissociate into ions:
C12H22O11 (s) → C12H22O11 (aq)
Since no ions are produced, sugar solutions do not conduct electricity, unlike ionic compounds like copper sulfate (CuSO4) or sodium chloride (NaCl), which dissociate and allow electrical current to pass.
Remember: "Ionic compounds conduct; covalent compounds don’t." This can help distinguish between conductors and insulators in solution.
6. Visual Suggestion
6. Visual Suggestion
Illustrate a setup comparing the conductivity of solutions: use a light bulb or voltmeter connected to two electrodes immersed in each solution (sugar, NaCl, CuSO4), showing that only ionic solutions light up.
📖 Factual Verification & Reference
📖 Factual Verification & Reference:
Verified against NCERT Class XII Chemistry, Chapter on Solutions.
Question 2 of 5 Live App Practice
Which one among the following is present inthe nettle leaf hairs that causes burning pain?
Detailed Solution:
Correct Answer
✓ Option A is correct. Methanoic acid is responsible for the burning pain caused by nettle hairs.
📖 Governing Law / Core Concept
The pain induced by nettle hairs is primarily due to the presence of methanoic acid (formic acid), with the molecular formula \( HCOOH \).
🧪 Step-by-Step Breakdown
Methanoic acid is released when the hair-like structures of the nettle plant penetrate the skin, resulting in a burning sensation.
\[ HCOOH \rightarrow H^+ + HCOO^- \]
As it dissociates in aqueous solution, it produces hydrogen ions (\( H^+ \)), which stimulate pain receptors in the skin.
🔍 Option Analysis
Option B: Ethanoic acid (acetic acid) is used in vinegar, but is not present in nettle.
Option C: Benzoic acid is used as a preservative and is not related to nettle stings.
Option D: Acetic acid (same as Ethanoic acid) doesn't cause the sting from nettles.
⚡ Mnemonic / Speed-Run
Remember "Methan- for the sting!" which links methanoic acid (formic acid) to its irritant effect.
6. Visual Suggestion
6. Visual Suggestion
A diagram showing a cross-section of a nettle leaf, highlighting the stinging hairs and the release of methanoic acid when the hair penetrates the skin.
📖 Factual Verification & Reference
📖 Factual Verification & Reference:
Verified against NCERT Class XII Chemistry, Chapter on Carboxylic Acids.
Question 3 of 5 Live App Practice
Which one among the following is known as Milk of Magnesia?
Detailed Solution:
Correct Answer
✓ Option D is correct. Milk of Magnesia is magnesium hydroxide.
📖 Governing Law / Core Concept
Milk of Magnesia, chemically known as magnesium hydroxide (\(Mg(OH)_2\)), functions as an antacid that neutralizes stomach acidity by the following reaction:
\[ Mg(OH)_2 + 2HCl \rightarrow MgCl_2 + 2H_2O \]
🧪 Step-by-Step Breakdown
Milk of Magnesia is a suspension of magnesium hydroxide in water. It acts as an antacid by reacting with hydrochloric acid present in the stomach, thereby reducing acidity.
Observation:
Appearance: White, milky solution.
pH Neutralization: Increases pH level, alleviating symptoms of indigestion.
🔍 Option Analysis
Other options consist of:
A: Magnesium bicarbonate - Exists in solution form but not as an antacid.
B: Magnesium carbonate - Used in different contexts, not a common antacid.
C: Magnesium sulphate - Known as Epsom salt, primarily used as a laxative.
⚡ Mnemonic / Speed-Run
Remember: "Milk of Magnesia = Magic for Your Stomach!"
6. Visual Suggestion
6. Visual Suggestion
A diagram illustrating the chemical structure of magnesium hydroxide along with its neutralization reaction with hydrochloric acid can enhance understanding.
📖 Factual Verification & Reference
📖 Factual Verification & Reference:
Verified against NCERT Class XI Chemistry, Chapter on pH and its Applications.
Question 4 of 5 Live App Practice
Which one of the following statements is NOT correct?
Detailed Solution:
✓
1. Correct Answer
Option B is correct. [The higher the hydrogen ion concentration in a solution, lower is its pH]
📖 Short Explanation
The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It is inversely related to hydrogen ion concentration, meaning higher hydrogen ion concentration equates to a lower pH value.
💡 3. Why Correct Answer is Correct
The concept of pH is defined as the negative logarithm of the hydrogen ion concentration of a solution. Mathematically, it is expressed as:
\[ \text{pH} = -\log_{10}[\text{H}^+]\]
Here, a higher concentration of H+ ions indicates a lower pH, confirming that pH is inversely related to hydrogen ion concentration.
❌ 4. Why Other Options are Wrong
•Option A: Correct as it describes the pH scale accurately.
•Option C: Correct since the pH scale ranges from 0 to 14.
•Option D: Correct as 'p' in pH does stand for 'potenz.'
⚡
NDA Speed-Run / Mnemonic Shortcut
Remember that as pH decreases by 1, the H+ concentration increases by a factor of 10. Hence, low pH means high acidity.
🎯
5. Key Learning Point
pH is inversely related to H+ concentration: higher H+ means lower pH.
6. Visual Suggestion
A representative diagram showing a graduated pH scale ranging from 0 to 14, with annotations indicating low pH corresponds to high hydrogen ion concentration and vice versa, which could be accompanied by example acids and bases.
Question 5 of 5 Live App Practice
For acid rain, the pH of rain water should be less than
Detailed Solution:
✓
1. Correct Answer
Option C is correct. For acid rain, the pH of rainwater must be less than 5.6.
📖 Short Explanation
Acid rain occurs when the pH of rainwater falls below 5.6, usually due to atmospheric pollutants like sulfur dioxide and nitrogen oxides reacting with water vapor to form acids.
💡 3. Why Correct Answer is Correct
The pH value is a measure of how acidic or basic a solution is. Pure water has a neutral pH of 7.0. Naturally occurring carbon dioxide in the atmosphere dissolves in rainwater, forming carbonic acid, which gives the rain a slightly acidic pH of about 5.6. However, when pollutants like sulfur dioxide and nitrogen oxides, often resulting from industrial emissions, combine with atmospheric moisture, they form sulfuric and nitric acids, respectively. This results in a lower pH level in rainwater, leading to acid rain when the pH falls below 5.6. Acid rain can have severe environmental consequences on soil, plants, aquatic systems, and infrastructure.
❌ 4. Why Other Options are Wrong
•Option A: pH 7.0 indicates neutrality, which is typical for pure water without any acidity.
•Option B: pH 6.6 is less acidic than rain with dissolved atmospheric CO2; hence, it is incorrect for acid rain, though it is closer.
•Option D: pH 8.0 is alkaline, not acidic, and cannot pertain to acid rain.
⚡
NDA Speed-Run / Mnemonic Shortcut
Remember 'Acid < 5.6' as a quick check for acidic environments linked to acid rain by associating the numerical value 5.6 with easy mnemonic phrases like "Acid is below 5.6, not above or even at 6".
🎯
5. Key Learning Point
Acid rain is identified by a pH level of less than 5.6, indicating its formation from pollutants reacting with atmospheric moisture, which lowers the pH.
6. Visual Suggestion
Create a diagram showing a cross-section of the atmosphere including sources of sulfur dioxide and nitrogen oxides, their reactions in the atmosphere, leading to acid formation, and the resultant acid rain impacting the earth.
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