Chemistry Miscellaneous PYQs – Chemistry, SSC & Railway

Correct Answer:
Correct Answer: Option 3 – Biochemistry
Explanation:
Biochemistry is the branch of chemistry that studies the chemical processes and substances (proteins, enzymes, metabolism, etc.) occurring within and related to living organisms/cells.

Bromine Water Test for Unsaturation
Ethene (an unsaturated hydrocarbon with a C=C double bond) reacts with bromine water in anaddition reaction, adding Br atoms across the double bond to form 1,2-dibromoethane.
The orange colour of bromine water is discharged as it reacts, so the bromine waterturns from orange to colourless. This is a standard test to distinguish saturated from unsaturated hydrocarbons.
Correct Answer: The bromine water changes from orange to colorless

Branch of Chemistry Dealing with Metals
Inorganic chemistrydeals with the properties and behaviour of inorganic compounds, including metals, minerals and metal-containing compounds (organometallic chemistry is a related sub-branch of inorganic chemistry).
• Biochemistry studies chemical processes in living organisms.
• Analytical chemistry deals with identification/quantification of substances.
• Physical chemistry studies physical principles underlying chemical systems.
Correct Answer: Inorganic chemistry

Wöhler's Synthesis of Urea
The 'vital force theory' held that organic compounds could only be produced by living organisms through a mysterious 'vital force,' and could not be synthesised in a laboratory from inorganic substances.
In 1828,Friedrich Wöhlerdisproved this theory by synthesisingurea(an organic compound found in urine) by heatingammonium cyanate(an inorganic salt) in the laboratory, showing that organic compounds can be made from inorganic starting materials without any 'vital force'.
Correct Answer: By preparing urea from ammonium cyanate

Answer: Option 1 – Robert Boyle.
•Robert Boylefirst used the term 'element'.

Answer: Option 4 – Calcium carbonate.
• CO₂ + Ca(OH)₂ →CaCO₃↓ (white) + H₂O.

Answer: Option 1 — Testing with bromine water
Bromine water(brown) is decolourised byunsaturatedcompounds (addition reaction) but not by saturated ones — the standard lab test → Option 1.

Topic: Coordination Chemistry
Alfred Werner(1866-1919) was a Swiss chemist.
He proposed theWerner's Theory of Coordination Compoundsin 1893.
Key contributions:
• Introduced concept of primary and secondary valencies
• Explained structure and bonding in coordination complexes
• Won Nobel Prize in Chemistry (1913) for this work
Other scientists: Dalton (Atomic Theory), Newton (Physics), Bunsen (Spectroscopy)
Answer: Option 1 → Alfred Werner

Law of Conservation of Mass
Discovered by:Antoine Lavoisier (1789)
States: Mass is neither created nor destroyed in chemical reactions.
Lavoisier proved this through careful quantitative experiments.
Answer: Option 3 → Antoine Lavoisier

Correct Answer: Because it does not react easily — Option (b)
Nitrogen (N₂) is chemically inert under normal atmospheric conditions primarily because of the extremely strong triple bond (N≡N) between its two atoms. The bond dissociation energy of N₂ is very high (~945 kJ/mol), making it one of the strongest diatomic bonds. This means nitrogen requires enormous energy to break apart and react with other elements. As a result, N₂ is highly stable and does not readily participate in chemical reactions at room temperature and pressure.
Option (a) Because it absorbs ultraviolet rays — Incorrect: Ozone (O₃) absorbs UV rays, not nitrogen. Nitrogen's inertness is due to its strong triple bond, not UV absorption.
Option (c) Because it is rare — Incorrect: Nitrogen is NOT rare — it makes up approximately 78% of Earth's atmosphere. Its inertness is due to its strong triple bond, not rarity.
Option (d) Because it forms ozone — Incorrect: Ozone is formed from oxygen (O₃), not nitrogen. Nitrogen does not form ozone.

When dilute hydrochloric acid reacts with calcium carbonate, carbon dioxide gas is evolved.
This gas when passed through limewater (calcium hydroxide solution) turns it milky due to formation of calcium carbonate.
When carbon dioxide is passed in excess, the milkiness disappears because soluble calcium hydrogen carbonate is formed.
Hence, the gas reacts with limewater forming calcium carbonate first, then excess CO2 converts it into calcium hydrogen carbonate, removing the milkiness.
Final answer: Option 3

Correct Answer: White (Option 4)
When CO₂ is passed through lime water [Ca(OH)₂], a white precipitate of calcium carbonate ( CaCO ₃) is formed:
CO₂ + Ca(OH)₂ → CaCO ₃↓ (white) + H₂O
This is the standard test for CO₂ — it turns lime water milky white.
Why other options are wrong:
Option 1 – Red precipitate is not formed in this reaction.
Option 2 – Green precipitate is not formed.
Option 3 – Blue precipitate is not formed. CaCO ₃ is characteristically white.

Correct Answer: Option 1 – Urea
In 1828, German chemist Friedrich Wohler synthesized Urea (an organic compound) from ammonium cyanate (an inorganic compound). This was a landmark achievement because it disproved the 'Vital Force Theory' (Vitalism), which held that organic compounds could only be produced by living organisms. Wohler's synthesis of urea proved that organic compounds can be made from inorganic precursors in a laboratory.
Why other options are wrong:
Option 2 (Methane): Methane was not used by Wohler to disprove vitalism.
Option 3 (Ethanol): Not the compound synthesized by Wohler for this purpose.
Option 4 (Ethylene): Not the compound associated with Wohler's disproof of the vital force theory.

Argon-40 (the dominant Argon isotope in Earth's atmosphere) is produced by the radioactive decay of Potassium-40 in Earth's crust.
Hence, the answer is Decay of K-40.