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. What happens to water’s vapor pressure when heated?
[A] It increases
[B] It decreases
[C] It first increases then decreases
[D] No change
Show Answer
Correct Answer: A [It increases]
Notes:
Vapor pressure of water increases as its temperature rises. At 25°C, water’s vapor pressure is approximately 23.8 mmHg, while at 100°C it reaches 760 mmHg. When a liquid is heated, kinetic energy of molecules grows, allowing more to escape as vapor and thus increasing vapor pressure.
3. Argon is the third most common gas in the Earth’s atmosphere, at 0.93%. This gas is generated due to decay of which among the following isotopes in the Earth’s crust ?
[A] K-40
[B] Ca-40
[C] Ca-48
[D] K-41
Show Answer
Correct Answer: A [K-40]
Notes:
Potassium-40 is a radioactive isotope of potassium with a long half-life of 1.251×10⁹ years. The decay of this particular isotope explains the large abundance of argon (0.93%) in the Earth’s atmosphere.
4. 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.
5. PAN (Peroxyacetyl nitrate) is a secondary gaseous compound found in _?
[A] Classical smog
[B] Volatile organic compound
[C] Photochemical smog
[D] Green manure
Show Answer
Correct Answer: C [ Photochemical smog]
Notes:
Third option is the correct answer
Photochemical smog is the chemical reaction of sunlight, nitrogen oxides and volatile organic compounds in the atmosphere, which leaves airborne particles and ground-level ozone.
6. The presence of which of the following chemical elements helps to differentiate between sweet and sour crude oil?
[A] Iron
[B] Sulphur
[C] Vanadium
[D] Chromium
Show Answer
Correct Answer: B [ Sulphur ]
Notes:
Crude oil with high amount of Sulphur is termed as sour and with less Sulphur is called the sweet grade. Sour grade crude requires extra processing cost.
7. Which among the following acids is generally used as a first hand test to judge whether a metal is Gold or not?
[A] Sulfuric Acid
[B] Nitric Acid
[C] Hydrochloric Acid
[D] Sulfurous Acid
Show Answer
Correct Answer: B [Nitric Acid]
Notes:
The funda is that when a small drop of a strong acid, such as nitric acid, is put onto the metal’s surface, most metals fizz or bubble, whilst precious metals (Gold or Platinum not silver) are unaffected.
8. Which of these methods is suitable to obtain the coloured component from black ink?
[A] Evaporation
[B] Sublimation
[C] Crystallisation
[D] All of the above
Show Answer
Correct Answer: A [Evaporation]
Notes:
The dye from water can be separated by the method of evaporation. Evaporation is used to separate the volatile component (solvent) from its non-volatile solute.
9. What do we call the region of space around the nucleus where the probability of finding an electron is maximum?
[A] Shell
[B] sub-shell
[C] Orbital
[D] electron cloud
Show Answer
Correct Answer: C [Orbital]
Notes:
The region of space around the nucleus where the probability of finding an electron is maximum is called an orbital. The electron cloud is a visual model that represents all the orbitals in an atom
10. Who correctly discovered or calculated for subatomic particles?
[A] John Dalton discovered electrons
[B] James Chadwick discovered protons
[C] Rutherford calculated charge to mass ratio of electrons
[D] None of the above
Show Answer
Correct Answer: D [None of the above]
Notes:
J.J. Thomson discovered electrons in 1897. Ernest Rutherford discovered protons in 1917. J.J. Thomson calculated the charge to mass ratio of electrons in 1897. James Chadwick discovered neutrons in 1932. John Dalton proposed the atomic theory in 1808 but did not discover electrons or protons.
