Chemistry MCQs
Chemistry Objective (Multiple Choice) General Knowledge Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examination.
1. Dalton’s name is associated with which of the following terms?
[A] Electron
[B] Proton
[C] Atom
[D] Neutron
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Correct Answer: C [Atom]
Notes:
John Dalton introduced the atomic theory into chemistry. The main points of Dalton’s atomic theory are (1) Elements are made of extremely small particles called atoms. (2) Atoms of a given element are identical in size, mass and other properties; atoms of different elements differ in size, mass and other properties.(3) Atoms cannot be subdivided, created or destroyed. (4) Atoms of different elements combine in simple whole-number ratios to form chemical compounds. (5) In chemical reactions, atoms are combined, separated or rearranged.
2. Which gas is produced when an alkali metal, like Lithium or Sodium, reacts with water?
[A] Oxygen
[B] Hydrogen
[C] Ozone
[D] Carbon Dioxide
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Correct Answer: B [Hydrogen]
Notes:
The reaction of alkali metals with water produces Hydrogen gas. These metals are part of the first group on the period table and include lithium, sodium, and potassium. They are known for their vigorous reactions with water, which results in the liberation of hydrogen gas. Along with the gas, this reaction also forms a basic alkali metal hydroxide, which gives the solution its characteristic basic or alkaline properties.
3. Which among the following is the lowest atomic number element without any stable isotopes?
[A] Technetium
[B] Molybdenum
[C] Ruthenium
[D] Niobium
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Correct Answer: A [Technetium]
Notes:
The correct answer is Technetium. It has the atomic number 43 and is the lowest atomic number element without any stable isotopes. All of its isotopes are radioactive, with Technetium-98 being the most stable, having a half-life of about 4.2 million years. Technetium was first artificially produced in 1937 by Carlo Perrier and Emilio Segrè, making it the first element to be artificially created.
4. Under standard conditions, which of the following is the most stable form of carbon?
[A] Charcoal
[B] Graphite
[C] Diamond
[D] Amorphous Carbon
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Correct Answer: B [Graphite]
Notes:
Under standard conditions, Graphite is the most stable form of carbon. It is commonly used in pencils and lubricants due to its layered structure. These layers can move over each other, making graphite soft and slippery. Besides Graphite, other forms of carbon are diamond, charcoal, and amorphous carbon, each with unique properties and applications.
5. What is the hemihydrate of calcium sulphate commonly known as?
[A] Gypsum
[B] Plaster of Paris
[C] Chloroform
[D] Limestone
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Correct Answer: B [Plaster of Paris]
Notes:
Plaster of Paris is the common name of calcium sulphate hemihydrate because half molecule of water is attached with calcium sulphate. The chemical formula of plaster of Paris is CaSO4.1/2H2O.
6. Which of the following is correct about Potassium carbonate?
[A] Its chemical formula is K CO3
[B] It is a salt which is white in colour
[C] It is used in the production of soap
[D] All of the above
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Correct Answer: D [All of the above]
Notes:
Potassium carbonate is a salt which is white in colour. It is used in the production of soap. Its chemical formula is K2 CO3.
7. Which of the following is correct about tincture of iodine?
[A] It is a solution of iodine in ethanol
[B] It is a solution of iodine in Hydrochloric acid
[C] It is a solution of iodine in Nitric acid
[D] None of the above
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Correct Answer: A [It is a solution of iodine in ethanol]
Notes:
A solution of iodine in alcohol known as ‘tincture of iodine’, has iodine (solid) as the solute and alcohol (liquid) as the solvent.
8. What do we call the region of space around the nucleus where the probability of finding an electron is maximum?
[A] Shell
[B] sub-shell
[C] Orbital
[D] electron cloud
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Correct Answer: C [Orbital]
Notes:
The region of space around the nucleus where the probability of finding an electron is maximum is called an orbital. The electron cloud is a visual model that represents all the orbitals in an atom
9. Which of the following decays represents the decay of Uranium-238 to thorium-234?
[A] Alpha decay
[B] Beta decay
[C] Gamma decay
[D] None of the above
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Correct Answer: A [Alpha decay]
Notes:
The radioactive decay of uranium-238 to thorium-234, with the emission of a helium nucleus, is a well-known example of alpha decay.
10. What do we call the reaction when an acid and a base react together to form salt and water?
[A] Reduction Reaction
[B] Oxidation Reaction
[C] Neutralisation Reaction
[D] Combination Reaction
Show Answer
Correct Answer: C [Neutralisation Reaction]
Notes:
When an acid and a base react together to form salt and water, the reaction is known as Neutralisation Reaction. HCl (aq) + NaOH (aq) ? H2O (l) + NaCl (aq) (acid) (base) (Water) (Salt) Hydrochloric acid Sodium hydroxide Sodium Chloride