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 substances is most suitable for making Compact Discs?
[A] PVC
[B] Polyethylene
[C] Polyamides
[D] Polycarbonates
Show Answer
Correct Answer: D [Polycarbonates
]
Notes:
Polycarbonate(PC) is a tough thermoplastic. It is not only highly transparent but also has good toughness which most of the other thermoplastics do not possess. For this reason, it is widely used for making CDs, Safety Goggles, Mixer jar lids etc.
2. 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.
3. Sodium bicarbonate decomposes above 70 °C, making it usable in bakery products. What end product of this thermal decomposition process contributes to its use in baking?
[A] Hydrogen
[B] Carbon Dioxide
[C] Water Vapor
[D] Sodium Carbonate
Show Answer
Correct Answer: B [Carbon Dioxide]
Notes:
Sodium bicarbonate, commonly known as baking soda, is used in baking due to its ability to decompose above 70 degrees Celsius and release carbon dioxide. This chemical reaction is given by the equation 2 NaHCO3 – Na2CO3 + H2O + CO2. In baking, it reacts with other ingredients or decomposes at high temperatures to produce carbon dioxide, which causes the dough to rise, creating the fluffy texture in baked goods.
4. Consider the following substances:
- Iodine
- Naphthalene
- Camphor
Which of the above substances undergo ‘sublimation’ on heating?
[A] Only 1 and 2
[B] All of them
[C] Only 2 and 3
[D] Only 1 and 3
Show Answer
Correct Answer: B [All of them]
Notes:
Sublimation is a transition from solid to gas, bypassing the liquid phase. Iodine sublimes, producing violet vapors; naphthalene sublimes, hence its use in mothballs; and camphor also sublimes, used in medicinal and aromatic applications. Thus, all three substances exhibit sublimation upon heating, making ‘All of them’ the correct answer.
5. 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.
6. Which of the following is incorrect?
[A] Alloying helps in improving the properties of a metal
[B] An alloy is a heterogeneous mixture of two or more metals
[C] The melting point of an alloy is less than that of pure metals
[D] All of the above
Show Answer
Correct Answer: B [An alloy is a heterogeneous mixture of two or more metals]
Notes:
An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal. Alloying helps in improving the properties of a metal. The melting point of an alloy is less than that of pure metals.
7. What is the change in the rate constant for a chemical reaction when temperature rises by 10° C?
[A] The rate constant is constant
[B] The rate constant is nearly doubled
[C] The rate constant is nearly halved
[D] The rate constant becomes four times
Show Answer
Correct Answer: B [The rate constant is nearly doubled]
Notes:
For a chemical reaction with rise in temperature by 10°, the rate constant is nearly doubled. Most of the chemical reactions are accelerated by increase in temperature.
8. From which element in the modern periodic table, the 3d transition series starts?
[A] Zinc
[B] Iron
[C] Scandium
[D] Copper
Show Answer
Correct Answer: C [Scandium]
Notes:
The 3d transition series starts from scandium (Z = 21) and completes at zinc (Z=30). Reason for this transition series is that before the 4p orbital is filled, filling up of 3d orbitals becomes energetically favourable.
9. Choose the correct statement about Litmus solution:
[A] Its colour is brown
[B] It is slightly acidic in nature
[C] It is extracted from lichen
[D] All of the above
Show Answer
Correct Answer: C [It is extracted from lichen]
Notes:
Litmus solution is purple in colour. It is neither acidic nor basic in nature. It is extracted from lichen, a plant belonging to the division Thallophyta, and is commonly used as an indicator.
10. What is the PH of human blood?
[A] 8.2
[B] 7.4
[C] 6.5
[D] 7
Show Answer
Correct Answer: B [7.4]
Notes:
Blood is normally slightly basic, with a normal pH range of 7.35 to 7.45. Usually the human body maintains the pH of blood close to 7.40.
