Chemistry MCQs
Chemistry Objective (Multiple Choice) General Knowledge Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examination.
1. Which among the following is the correct set of chemical formulae of Chile Saltpetre, Saltpetre and Quick Lime?
[A] KNO3, NaNO3, CaO
[B] NaNO3, KNO3, Ca(OH)2
[C] Na(OH)2, KOH, CaO
[D] NaNO3, KNO3, CaO
Show Answer
Correct Answer: D [NaNO3, KNO3, CaO]
Notes:
Saltpetre, also spelled Saltpeter, also called Nitre, or Niter, any of three naturally occurring nitrates, distinguished as (1) ordinary saltpetre, or potassium nitrate, KNO3; (2) Chile saltpetre, cubic nitre, or sodium nitrate, NaNO3; and (3) lime saltpetre, wall saltpetre, or calcium nitrate, Ca(NO3)2.
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound.
2. Which among the following oxides cause the Acid rain?
[A] Carbon monoxide and carbon dioxide
[B] Nitrous oxide and sulphur dioxide
[C] Carbon dioxide and nitrous oxide
[D] Sulphur dioxide and carbon monoxide
Show Answer
Correct Answer: B [Nitrous oxide and sulphur dioxide ]
Notes:
Acid rain is caused by nitrous oxides (NOx) and sulfur dioxide (SO2) emissions, which react with water molecules in the atmosphere to form nitric and sulfuric acids. These acids then fall to the ground in rain, snow, fog, or dust particles.
3. “Atoms can neither be created nor destroyed.” This principle was given by __?
[A] Avogadro
[B] Dalton
[C] Rutherford
[D] Niels Bohr
Show Answer
Correct Answer: B [Dalton]
Notes:
The given principle is one of the postulates of the Dalton’s atomic theory given in 1803 by John Dalton. The postulates of Dalton’s atomic theory are as follows:
1. Elements consist of indivisible small particles (atoms).
2. All atoms of the same element are identical; different elements have different types of atom.
3. Atoms can neither be created nor destroyed.
4. ‘Compound elements’ (i.e. Compounds) are formed when atoms of different elements join in simple ratios to form ‘compound atoms’ (i.e. Molecules).
4. What happens to ozone’s volume when it is heated?
[A] Increases
[B] Decreases
[C] Remains unchanged
[D] First increases, then decreases
Show Answer
Correct Answer: A [Increases]
Notes:
According to Charles’s Law, for gases at constant pressure, volume increases with temperature. Heating ozone increases the kinetic energy of molecules, expanding its volume if pressure is constant. Ozone (O₃) behaves like other gases, expanding when heated. This law applies to all ideal gases and ozone approximates ideal behavior under moderate conditions.
5. What characteristic of silica gel, a granular form of silica produced from sodium silicate, enables it to control humidity and prevent spoilage or degradation when packaged with various products?
[A] Its high thermal conductivity
[B] Its hygroscopic properties
[C] Its high reflectivity
[D] Its low thermal conductivity
Show Answer
Correct Answer: B [Its hygroscopic properties]
Notes:
Silica gel possesses hygroscopic properties, meaning it can absorb and hold water vapour. This makes it an effective desiccant or drying agent. When packaged with products, silica gel can help control humidity and prevent spoilage or degradation by absorbing excess moisture. This property is particularly valuable when shipping or storing items that can be negatively impacted by damp conditions, like electronics, food, and leather goods.
6. Why most of the aromatic hydrocarbons burn with a sooty flame?
[A] Because the carbon-hydrogen ratio in aromatic compounds is high
[B] Because of the presence of the strong carbon-carbon bonds
[C] Because, hydrocarbons are unsaturated
[D] Because the carbon-hydrogen ratio in aromatic compounds is low
Show Answer
Correct Answer: A [ Because the carbon-hydrogen ratio in aromatic compounds is high]
Notes:
Because the carbon-hydrogen ratio in aromatic compounds is high.
7. Which of the following radical is also known as the “atmospheric detergent” ?
[A] Chlorine radical
[B] Hydroxyl radical
[C] Methyl radical
[D] Ozone radical
Show Answer
Correct Answer: B [ Hydroxyl radical]
Notes:
One of the most important chemical components of the troposphere is the ‘hydroxyl radical’: a highly reactive substance composed of an oxygen and a hydrogen atom, denoted ‘OH’. Hydroxyl radicals react with just about any other trace gas they encounter, removing them from the atmosphere.For example, OH combines with toxic carbon monoxide to generate carbon dioxide. In this sense, OH ‘cleans up’ the troposphere, and is sometimes called the detergent of the atmosphere.
8. Which of the following is not an isotope of Hydrogen?
[A] Protium
[B] Para hydrogen
[C] Deuterium
[D] Tritium
Show Answer
Correct Answer: B [ Para hydrogen]
Notes:
The three most stable isotopes of hydrogen: Protium, Deuterium and Tritium. Para hydrogen is not an isotope of hydrogen. Molecules of hydrogen in which the spins of both the nuclei are in the opposite direction are called Para hydrogen.
9. Which of the following chemicals is also known as “Chinese snow”?
[A] Silver iodide
[B] Potassium nitrate
[C] Ammonium chloride
[D] Sodium phosphate
Show Answer
Correct Answer: B [ Potassium nitrate]
Notes:
Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpetre or saltpetre. It is also known as “Chinese snow”. Major uses of potassium nitrate are in fertilizers, rocket propellants and fireworks.
10. Which of the following chemicals is used as a molecular sieve to filter common salts from seawater to produce potable water?
[A] Graphene oxide
[B] Phosgene
[C] Sodium hypochlorite
[D] Calcium carbonate
Show Answer
Correct Answer: A [ Graphene oxide]
Notes:
Graphene oxide is used as a molecular sieve to filter common salts from seawater to produce potable water.
