1. Acids
Acid: substance which gives H⁺ ions in solution and tastes sour.
Examples:
- Hydrochloric acid (HCl) – in stomach
- Sulphuric acid (H₂SO₄) – car batteries, industry
- Natural/organic acids: citric acid (lemon), acetic acid (vinegar), tartaric acid (tamarind)
2. Bases
Base: substance which gives OH⁻ ions in solution; feels soapy, bitter.
Examples:
- NaOH (sodium hydroxide)
- KOH (potassium hydroxide)
- Ca(OH)₂ (slaked lime)
3. Salts
Salt: product formed when an acid reacts with a base.
General: Acid + Base → Salt + Water
Examples:
- HCl + NaOH → NaCl (common salt) + H₂O
- H₂SO₄ + CuO → CuSO₄ + H₂O
हिंदी: Acid + Base → Salt + Water
खट्टा + कड़वा = नमक + पानी (simplified way to remember).
4. Indicators & pH (basic idea)
- Indicators show whether a solution is acidic or basic.
- Litmus: red in acid, blue in base.
- Turmeric: yellow in acid, reddish-brown in base.
- Phenolphthalein: colourless in acid, pink in base.
- pH scale: measure of acidity/basicity (0–14).
- pH < 7 → acidic
- pH = 7 → neutral
- pH > 7 → basic
5. Oxidation & Reduction (UPSC asks this definition)
- Oxidation: addition of oxygen or removal of hydrogen.
- Reduction: removal of oxygen or addition of hydrogen.
हिंदी Trick:
Oxygen मिले → Oxidation, Oxygen छूटे → Reduction
📘 Practice Questions (NDA Style)
1. Which of the following is an acid?
a) NaOH
b) HCl
c) Ca(OH)₂
d) NH₃
2. Litmus paper turns red in:
a) Base
b) Acid
c) Salt
d) Distilled water
3. Acid + Base gives:
a) Acid only
b) Base only
c) Salt and water
d) Gas only
4. On pH scale, a solution with pH 2 is:
a) Strongly acidic
b) Weakly acidic
c) Neutral
d) Basic
5. In the reaction CuO + H₂ → Cu + H₂O, hydrogen is:
a) Oxidised
b) Reduced
c) Neutral
d) Decomposed
a) NaOH
b) HCl
c) Ca(OH)₂
d) NH₃
2. Litmus paper turns red in:
a) Base
b) Acid
c) Salt
d) Distilled water
3. Acid + Base gives:
a) Acid only
b) Base only
c) Salt and water
d) Gas only
4. On pH scale, a solution with pH 2 is:
a) Strongly acidic
b) Weakly acidic
c) Neutral
d) Basic
5. In the reaction CuO + H₂ → Cu + H₂O, hydrogen is:
a) Oxidised
b) Reduced
c) Neutral
d) Decomposed
Answers:
1 – b
2 – b
3 – c
4 – a
5 – a
1 – b
2 – b
3 – c
4 – a
5 – a
Quick Recap | सार
Now you should be able to:
- Recall the most important ideas of this topic.
- Solve typical NDA-style questions from this chapter.
- Spot and avoid common traps used in competitive exams.
Self-check: 3–4 random questions उठा कर देखिए – अगर आसानी से हो रहे हैं, तो chapter strong है।
Common Exam Mistakes | आम गलतियाँ
- Concept ठीक से clear न करना और सीधे रटने की कोशिश करना।
- Question पूरी तरह पढ़े बिना answer mark कर देना।
- Figures, dates, या formulas को last step में verify न करना।
NDA में smart strategy यह है कि आसान वाले सवाल पहले, doubtful बाद में – और silly mistakes से बचना सबसे ज़रूरी है।