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 of the following is the poorest conductor of heat in comparison to other options?
[A] Silver
[B] Copper
[C] Lead
[D] Mercury
Show Answer
Correct Answer: C [ Lead ]
Notes:
Silver is best conductor of heat while among metals lead is poorest conductor of heat. Cooper and aluminum are good conductor while mercury is a poor conductor.
2. What is the number of naturally occurring Halogens in the periodic table?
[A] 3
[B] 4
[C] 5
[D] 6
Show Answer
Correct Answer: C [5]
Notes:
fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At)
3. Which among the following allotropes of Oxygen is found in 6 phases under various pressures and temperatures?
[A] Ozone
[B] Tetra oxygen
[C] Octaoxygen
[D] None of them
Show Answer
Correct Answer: C [Octaoxygen]
Notes:
The correct answer is Octaoxygen. Octaoxygen (O8) is an allotrope of oxygen that can exist in multiple phases under varying pressures and temperatures. It was first synthesized in 2001 and is notable for its unique molecular structure, which consists of eight oxygen atoms. Ozone (O3) is well-known but does not exhibit multiple phases like octaoxygen. Tetraoxygen (O4) is less stable and not commonly referenced in the same context.
4. Which among the following makes Chile saltpetre different from saltpetre?
[A] Nitrate
[B] Sodium
[C] Magnesium
[D] Calcium
Show Answer
Correct Answer: B [Sodium]
Notes:
Chile saltpetre, or sodium nitrate (NaNO3), differs from regular saltpetre, which typically refers to potassium nitrate (KNO3). Chile saltpetre is primarily composed of sodium, while traditional saltpetre contains potassium. Historically, Chile saltpetre was extensively mined in the Atacama Desert and was crucial for fertilizer and explosives in the 19th century.
5. If a Hydrogen atom is removed from a hydrocarbon of Benzene group, the remaining residue is called _________?
[A] Alkyl
[B] Aryl
[C] Arene
[D] Azene
Show Answer
Correct Answer: B [Aryl]
Notes:
The correct answer is Aryl. In organic chemistry, when a hydrogen atom is removed from a benzene ring (a hydrocarbon), the remaining structure is referred to as an aryl group. Aryl groups are derived from aromatic compounds, specifically those containing a benzene ring. For example, when a hydrogen is removed from toluene (methylbenzene), the resulting aryl group is called a tolyl group. Aryl groups are important in various chemical reactions and are foundational in the synthesis of many organic compounds.
6. Acid rain is capable of damaging the buildings and historic monuments which are made up of rocks such as limestone and marble. Which among the following is the end product of such reaction?
[A] Quick Lime
[B] Calcium Carbonate
[C] Calcium Hydroxide
[D] Gypsum
Show Answer
Correct Answer: D [Gypsum]
Notes:
When sulfuric, and nitric acids, present in the acid rain reacts with the calcite in marble and limestone, it get dissolve and formed gypsum and washed off by the water. The rain can dissolve limestone and marble through direct contact.
7. Which among the following is the correct impact of the London Forces in the Cycloalkanes?
[A] The melting and boiling points get increased
[B] The Melting and boiling points get decreased
[C] There is not impact on the melting and boiling points
[D] The melting point increases but boiling point decreases
Show Answer
Correct Answer: A [The melting and boiling points get increased]
Notes:
Please note that the Cycloalkanes with more than 20 carbon atoms are called Cycloparaffins. The cycloalkanes have the same properties as the alkanes but they have `Higher Boiling & Melting points`. This is because of the stronger dispersion forces between the atoms known as London Forces.
8. Which of the following is the correct order of composition of biogas released through anaerobic bio-digester system?
[A] Methane> Carbon dioxide> Nitrogen> Hydrogen
[B] Carbon dioxide> Nitrogen> Methane> Hydrogen
[C] Nitrogen> Hydrogen> Carbon dioxide> Methane
[D] Hydrogen> Nitrogen> Methane> Carbon dioxide
Show Answer
Correct Answer: A [ Methane> Carbon dioxide> Nitrogen> Hydrogen ]
Notes:
The correct composition of biogas released through anaerobic bio-digester system is:
Methane (CH4) – 50–75 %
Carbon dioxide (CO2) – 25–50%
Nitrogen (N2) – 0–10%
Hydrogen (H2) – 0–1%
Hydrogen sulphide (H2S) – 0–3%
9. The largest component of Coal gas is__?
[A] Methane
[B] Hydrogen
[C] Carbon Dioxide
[D] Carbon Monoxide
Show Answer
Correct Answer: B [ Hydrogen]
Notes:
Typical composition of the Coal gas is as follows: •Hydrogen 50% •Methane 35% •Carbon monoxide 10% •Ethylene 5%
10. 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.
