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 are the most and the least electronegative elements in the periodic table?
[A] Fluorine and Caesium
[B] Hydrogen and Helium
[C] Carbon and Oxygen
[D] Chlorine and Fluorine
Show Answer
Correct Answer: A [Fluorine and Caesium]
Notes:
Caesium is the least electronegative element in the periodic table and Fluorine is the most electronegative. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
2. Which of the following does not increase when we move from left to right along a period in the periodic table?
[A] Oxidising Power of elements
[B] Electronegativity
[C] Non-metallic Character
[D] Reducing power
Show Answer
Correct Answer: D [Reducing power]
Notes:
The oxidizing power of elements increases on moving left to right along a period in the periodic table. This is because electronegativity and the non-metallic character increases from left to right.
3. Which among the following elements are generally find in free state?
[A] Group 11 elements
[B] Group 12 elements
[C] Group 13 elements
[D] Group 14 elements
Show Answer
Correct Answer: A [Group 11 elements ]
Notes:
Group 11 is also known as the coinage metals, due to their former usage. They were most likely the first three elements discovered. Copper, silver, and gold all occur naturally in elemental form.
4. Which among the following is the objective of the Methyl tert-butyl ether (MTBE) mixing with Petroleum?
[A] Raise Octane Number
[B] Antioxidant Stabilizer
[C] Lead Scavanger
[D] Fuel Dye
Show Answer
Correct Answer: A [Raise Octane Number ]
Notes:
MTBE is a gasoline additive, used as an oxygenate to raise the octane number. Its use is controversial in the US and declining in that country in part because of its occurrence in groundwater and legislation favoring ethanol.
5. 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.
6. Calcium Magnesium Silicate is commonly called as ________?
[A] Asbestos
[B] Borax
[C] Baking Soda
[D] Washing Soda
Show Answer
Correct Answer: A [Asbestos]
Notes:
CaMgO4Si is the chemical formula of calcium magnesium silicate . Calcium magnesium silicate is commonly known as Asbestos. Asbestos is a fibrous silicate mineral as the substance is formed by miniature crystal fibers, these crystal are loosely attached releasing dust of silicate crystal upon small touch.
7. F block elements in the periodic table which are commonly called Lanthanides have the following atomic numbers:
[A] 57-70
[B] 57-71
[C] 58-71
[D] 58-70
Show Answer
Correct Answer: B [57-71]
Notes:
The correct answer is 2. The lanthanides are a series of 15 elements in the periodic table, from atomic numbers 57 (Lanthanum) to 71 (Lutetium). They are known for their similar properties and are often found together in nature. The range of atomic numbers for lanthanides is 57 to 71, not 57-70 or 58-70.
8. Which among the following will undergo a chemical reaction depending on the pH of the solution?
[A] Calcium Oxide
[B] Zinc Oxide
[C] Ferric Oxide
[D] Ferrous Oxide
Show Answer
Correct Answer: B [Zinc Oxide]
Notes:
Zinc oxide (ZnO) can undergo a chemical reaction depending on the pH of the solution. In acidic conditions, it can react to form zinc ions (Zn²⁺), while in alkaline conditions, it can form zincates. This behavior is due to its amphoteric nature, which allows it to react with both acids and bases. In contrast, calcium oxide (CaO) is basic, ferric oxide (Fe₂O₃) is generally inert in neutral pH, and ferrous oxide (FeO) is less reactive in varying pH levels.
9. How many parts are of other metals in a 17 carat Gold?
[A] 3
[B] 5
[C] 7
[D] 9
Show Answer
Correct Answer: C [7]
Notes:
In 17 carat gold, the composition is 17 parts gold and 7 parts other metals, making it 70.6% gold. The term “carat” refers to the purity of gold, with 24 carats being pure gold. Thus, 17 carat gold contains 7 parts of other metals, which can include copper, silver, or palladium, used to enhance durability and alter color.
10. 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.
