NDA Chemistry
NDA Chemistry: Acids, Bases & Salts Guide
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:
Acid-Base Theories
- Arrhenius Theory: Acids release $H^+$ ions in aqueous solution; Bases release $OH^-$ ions.
- 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.
🔍 Option Analysis
- A: Copper sulphate (CuSO4) - Ionic compound, conducts electricity when dissolved.
- B: Sodium chloride (NaCl) - Ionic compound, conducts electricity when dissolved.
- C: Sugar (C12H22O11) - Non-ionic, does not conduct electricity.
- D: Sodium hydroxide (NaOH) - Ionic compound, conducts electricity when dissolved.
⚡ Mnemonic / Speed-Run
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 of the following is an organic acid ?
Detailed Solution:
Correct Answer
✓ Option C is correct. Acetic acid is the only organic acid among the options.
📖 Governing Law / Core Concept
Organic acids are typically characterized by the presence of a carboxyl group (-COOH) in their molecular structure. Acetic acid, or ethanoic acid, is one such acid.
🧪 Step-by-Step Breakdown
1. Hydrochloric acid (HCl): An inorganic strong acid.
2. Nitric acid (HNO₃): Another inorganic strong acid.
3. Acetic acid (CH₃COOH): An organic acid, derived from vinegar.
4. Sulphuric acid (H₂SO₄): A highly strong inorganic acid.
🔍 Option Analysis
- Hydrochloric acid (A): Inorganic acid, significant in digestion.
- Nitric acid (B): Inorganic, used in fertilizers.
- Acetic acid (C): Organic acid, used in food preservation.
- Sulphuric acid (D): Industrial inorganic acid, used in batteries.
⚡ Mnemonic / Speed-Run
To remember which acids are organic, recall "ACiD - Acetic is Chemical Derived," emphasizing that only acetic acid fits the organic category.
📖 Factual Verification & Reference
📖 Factual Verification & Reference:
Verified against NCERT Class 11 Chemistry, Chapter on Organic Compounds.
Question 3 of 5
Live App Practice
The pH value of Milk of Magnesia is approximately
Detailed Solution:
Correct Answer
✓ Option C is correct. Milk of Magnesia is a basic suspension.
📖 Governing Law / Core Concept
Milk of Magnesia primarily consists of magnesium hydroxide \((Mg(OH)_2)\), which is a weak base. Its pH typically ranges between 10 and 11.
🧪 Step-by-Step Breakdown
The pH scale measures the acidity or basicity of a solution, with values below 7 indicating acids, 7 indicating neutrality, and above 7 indicating bases.
The reaction for magnesium hydroxide in water is:
\[
Mg(OH)_2 (s) \leftrightarrow Mg^{2+} (aq) + 2 OH^- (aq)
\]
The production of hydroxide ions \((OH^-)\) increases the basicity of the solution, resulting in a pH value near 10.
\[
\text{pH} = -\log [H^+]
\]
Given that the concentration of hydroxide ions is high, the resulting concentration of hydrogen ions \([H^+]\) is low, thereby confirming a basic pH.
🔍 Option Analysis
- **A: Zero** - This suggests a strong acid, which is not applicable here.
- **B: 7** - Indicates neutrality, but Milk of Magnesia is basic.
- **C: 10** - Correct, as this indicates a basic solution.
- **D: 14** - This indicates a strong base, which does not align with the characteristics of Milk of Magnesia.
⚡ Mnemonic / Speed-Run
Remember that "Milk of Magnesia" = "Magnesium Hydroxide" = "Basic Solution" (pH around 10).
6. Visual Suggestion
6. Visual Suggestion
Consider a pH scale diagram highlighting Milk of Magnesia at pH 10, showing how it compares with neutral and acidic solutions.
📖 Factual Verification & Reference
📖 Factual Verification & Reference:
Verified against NCERT Class XII Chemistry, Chapter on Acids, Bases, and Salts.
Question 4 of 5
Live App Practice
Which one of the following acids is predominantly found in tomatoes?
Detailed Solution:
Correct Answer
✓ Option C is correct. Oxalic acid is the predominant acid found in tomatoes.
📖 Governing Law / Core Concept
Oxalic acid (\(C_2H_2O_4\)) is a naturally occurring dicarboxylic acid found in various plants as a method of regulating calcium levels within the plant. It acts as a metabolite.
🧪 Step-by-Step Breakdown
In tomatoes, oxalic acid contributes to the tart flavor and is a part of various metabolic pathways. When ingested, it can react with calcium ions to form calcium oxalate:
\[ C_2H_2O_4 + Ca^{2+} \rightarrow CaC_2O_4 \downarrow + 2H^+ \]
This leads to the formation of a precipitate (calcium oxalate), which may appear in various foods.
🔍 Option Analysis
A: Acetic acid, found in vinegar, primarily contributes to sourness but is not predominant in tomatoes.
B: Tartaric acid is associated with grapes and cream of tartar, not tomatoes.
D: Lactic acid is produced in fermented foods, like yogurt, and is not characteristic of tomatoes.
⚡ Mnemonic / Speed-Run
To remember the acids: A for Acetic (Vinegar), T for Tartaric (Grapes), O for Oxalic (Spinach, Tomatoes), L for Lactic (Dairy).
6. Visual Suggestion
6. Visual Suggestion
A comparison table showing the presence of various acids in different fruits and vegetables, emphasizing the relative content of oxalic acid in tomatoes.
📖 Factual Verification & Reference
📖 Factual Verification & Reference:
Verified against NCERT Class XI Chemistry, Chapter on Organic Compounds.
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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