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 also known as wood alcohol?
[A] Methanol
[B] Ethanol
[C] Propanal
[D] Butanol
Show Answer
Correct Answer: A [Methanol]
Notes:
Methanol (CH3OH) is also known as Wood Alcohol. It’s a solvent in many chemical processes and is a component of automobile antifreeze.
2. What happens to the weight of Iron, when it rusts?
[A] Increases for long time
[B] Decreases then increases
[C] Increases then decreases
[D] Remains the same
Show Answer
Correct Answer: C [Increases then decreases]
Notes:
When iron or any other metal oxidizes, oxygen from the air combines with the iron to make iron oxide or rust. So, weight of the bar increases, due to the increased weight of oxygen which has combined with the iron. over time, the weight of the iron bar will tend to decrease, due to factors related more to erosion than to chemistry.
3. Which among the following is a common salt in Detergents?
[A] Sulphate
[B] Nitrate
[C] Sulphonate
[D] Carbonate
Show Answer
Correct Answer: A [Sulphate]
Notes:
Sodium sulfate, used as a filler in detergent powder, enables the adjustment of the concentration of the active matter in the detergent, as required.
4. 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.
5. Which of the following alkali metal ions has the highest hydration enthalpy?
[A] Lithium
[B] Sodium
[C] Potassium
[D] Caesium
Show Answer
Correct Answer: A [Lithium]
Notes:
Lithium ions has maximum degree of hydration and for this reason lithium salts are mostly hydrated.
6. Which of the following is correct about ozone?
[A] it is a red coloured gas
[B] it is odourless
[C] it is harmless in small concentrations
[D] All of the above
Show Answer
Correct Answer: C [it is harmless in small concentrations]
Notes:
Pure ozone is a pale blue gas, dark blue liquid and violet-black solid. Ozone has a characteristic smell and in small concentrations it is harmless. However, if the concentration rises above about 100 parts per million, breathing becomes uncomfortable resulting in headache and nausea.
7. What is the relationship between half-life period and initial concentration of the reacting species for a first order reaction?
[A] Both are directly proportional to each other
[B] Both are inversely proportional to each other
[C] Both are independent of each other
[D] The half life is twice the concentration of reacting species
Show Answer
Correct Answer: C [Both are independent of each other]
Notes:
For a first order reaction, half-life period is constant, i.e., it is independent of initial concentration of the reacting species. for a zero order reaction, it is directly proportional to the initial concentration of the reactants and inversely proportional to the rate constant. .
8. Which of the following is correct about Mendeleev’s Periodic Table?
[A] Argon is placed before Potassium
[B] Cobalt is placed before Nickel
[C] Tellurium is placed before iodine
[D] All of the above
Show Answer
Correct Answer: D [All of the above]
Notes:
All statements represent the anomalous pairs of elements in Mendeleev’s Periodic Table. The atomic mass of argon is 39.9 and that of potassium 39.1. But argon is placed before potassium in the periodic table. Similarly, Tellurium is placed before iodine and Cobalt is placed before Nickel.
9. What is the process known as where acids produce ions when dissolved in water?
[A] Vulcanisation
[B] Dissociation
[C] Scattering
[D] None of the above
Show Answer
Correct Answer: B [Dissociation]
Notes:
When an acid dissolves in water, a covalent bond between an electronegative atom and a hydrogen atom is broken by heterolytic fission. It gives out a proton (H+) and a negative ion. This process is called as Disassociation.
10. Where does the oxidation takes place in a Galvanic cell?
[A] Anode
[B] Cathode
[C] Oxidation does not take place
[D] None of the above
Show Answer
Correct Answer: A [Anode]
Notes:
In a galvanic cell, the half-cell in which oxidation takes place is called anode and it has a negative potential with respect to the solution. The other half-cell in which reduction takes place is called cathode and it has a positive potential with respect to the solution.
