UPSC Geoscientist

41. What is the number of moles of carbon in a sample containing 72.06 g o

What is the number of moles of carbon in a sample containing 72.06 g of carbon?

4
6
2
8
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To find the number of moles of a substance, you divide the mass of the substance by its molar mass. The molar mass of carbon (C) is approximately 12.01 g/mol. Given the mass of carbon as 72.06 g, the number of moles is calculated as:
Number of moles = Mass / Molar Mass = 72.06 g / 12.01 g/mol ≈ 6.00 moles.
– The number of moles relates mass to the number of particles (atoms or molecules).
– Molar mass is the mass of one mole of a substance.
– The atomic mass of Carbon (C) is the basis for its molar mass.
The unit “mole” is the SI unit for the amount of substance. One mole contains approximately 6.022 x 10^23 particles (Avogadro’s number). The atomic mass unit (amu) is defined such that the atomic mass of Carbon-12 is exactly 12 amu. The molar mass in grams per mole is numerically equal to the atomic mass in amu.

42. Which one of the following statements about the law of chemical combin

Which one of the following statements about the law of chemical combination is not correct?

Equal volumes of all gases at the same temperature and pressure contain equal number of molecules.
If two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of other element, are not in any proportion.
Matter can neither be created nor destroyed.
A given compound always contains exactly the same proportion of elements by weight.
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The correct answer is that statement B is not correct.
The Law of Chemical Combination includes fundamental principles like the Law of Conservation of Mass, Law of Definite Proportions, and Law of Multiple Proportions.
Statement A describes Avogadro’s Law, a key principle relating to gases in chemical reactions. Statement C is the Law of Conservation of Mass. Statement D is the Law of Definite Proportions (or Constant Composition). Statement B contradicts the Law of Multiple Proportions, which states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in a ratio of small whole numbers. The statement B says they are “not in any proportion”, which is false.

43. What are the major raw materials used in the manufacture of cement?

What are the major raw materials used in the manufacture of cement?

Limestone and clay
Al<sub>2</sub>O<sub>3</sub> and limestone
Fe<sub>3</sub>O<sub>4</sub> and clay
Clay and MgO
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The correct answer is Limestone and clay.
Cement is manufactured by heating a mixture of calcareous materials (primarily calcium carbonate from limestone) and argillaceous materials (clay or shale containing silica, alumina, and iron oxide).
Limestone (providing CaO) and clay (providing SiO₂, Al₂O₃, Fe₂O₃) are the two main raw materials used in the production of Portland cement. They are mixed in specific proportions and heated in a kiln to produce cement clinker, which is then ground into the final product.

44. Match List-I with List-II and select the correct answer using the code

Match List-I with List-II and select the correct answer using the code given below the Lists :

List-I
(Compound)		 List-II
(Use)
A. Bleaching powder 1. Removal of permanent hardness of water
B. Baking soda 2. Making toys
C. Washing soda 3. Ingredient in antacids
D. Plaster of Paris 4. Disinfecting drinking water
A-2, B-3, C-1, D-4
A-4, B-1, C-3, D-2
A-2, B-1, C-3, D-4
A-4, B-3, C-1, D-2
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The correct answer is A-4, B-3, C-1, D-2.
Matching the compounds with their common uses.
Bleaching powder (Calcium hypochlorite) is used as a disinfectant for water (A-4). Baking soda (Sodium bicarbonate) is an ingredient in antacids due to its alkaline nature (B-3). Washing soda (Sodium carbonate) is used to precipitate calcium and magnesium ions, thus removing permanent hardness of water (C-1). Plaster of Paris (Calcium sulfate hemihydrate) hardens upon mixing with water and is used for making casts, statues, and toys (D-2).

45. Which one of the following statements regarding gold is not correct?

Which one of the following statements regarding gold is not correct?

24 karat gold is very soft.
22 karat gold is generally used to make ornaments.
22 karat gold contains 22 parts of pure gold and 2 parts of iron to make it hard.
18 karat gold comprises of 75% gold mixed with 25% of copper or silver to make it hard.
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The correct answer is that statement C is not correct.
Karat is a measure of gold purity. Pure gold (24 karat) is soft. Gold for jewelry is typically alloyed with other metals like copper, silver, or zinc to increase its hardness and durability.
Statement A is correct: 24 karat gold is pure and very soft. Statement B is correct: 22 karat gold (approx 91.67% pure) is commonly used for making ornaments. Statement D is correct: 18 karat gold is 18/24 = 75% gold, mixed with 25% other metals like copper or silver. Statement C is incorrect because while 22 karat gold contains 22 parts gold and 2 parts alloy, the alloy metals are typically copper, silver, or zinc, not predominantly iron. Iron is not a common alloying metal for standard gold jewelry due to issues like rusting and brittleness.

46. A sealed container contains one mole of helium and three moles of nitr

A sealed container contains one mole of helium and three moles of nitrogen gas at 25 °C. If the total pressure is 80000 Pa, what will be the partial pressure of nitrogen gas in the container?

20000 Pa
40000 Pa
60000 Pa
80000 Pa
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The correct answer is 60000 Pa.
According to Dalton’s Law of Partial Pressures, the partial pressure of a gas in a mixture is equal to its mole fraction multiplied by the total pressure of the mixture.
Total moles of gas = Moles of Helium + Moles of Nitrogen = 1 mole + 3 moles = 4 moles. The mole fraction of nitrogen is (Moles of Nitrogen) / (Total moles) = 3 / 4. The total pressure is 80000 Pa. Partial pressure of nitrogen = (Mole fraction of nitrogen) * (Total pressure) = (3/4) * 80000 Pa = 3 * 20000 Pa = 60000 Pa.

47. What is the maximum number of electrons that can be accommodated in th

What is the maximum number of electrons that can be accommodated in the M shell of an atom?

32
18
8
2
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The correct answer is 18.
The maximum number of electrons that can be accommodated in an electron shell is given by the formula 2n², where ‘n’ is the principal quantum number of the shell.
Electron shells are denoted by K, L, M, N, … corresponding to principal quantum numbers n = 1, 2, 3, 4, … respectively. For the M shell, n=3. Therefore, the maximum number of electrons in the M shell is 2 * (3)² = 2 * 9 = 18.

48. Which one of the following elements exhibits singular valency?

Which one of the following elements exhibits singular valency?

Sulphur
Phosphorus
Sodium
Copper
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The correct answer is Sodium.
Valency is the combining capacity of an element. Some elements have a fixed valency (singular), while others exhibit variable valency.
Sodium (Na) is an alkali metal (Group 1) and typically loses one electron to form a +1 ion, exhibiting a fixed valency of 1. Sulphur (S) can have valencies of 2, 4, 6. Phosphorus (P) can have valencies of 3, 5. Copper (Cu) is a transition metal and commonly exhibits valencies of 1 and 2. Thus, sodium is the element among the options that exhibits a singular valency.

49. Which one of the following elements is not monatomic?

Which one of the following elements is not monatomic?

Hydrogen
Helium
Neon
Argon
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The correct answer is Hydrogen.
Monatomic elements exist as single atoms under normal conditions. Noble gases (Group 18) are typically monatomic.
Helium (He), Neon (Ne), and Argon (Ar) are noble gases and exist as stable, single atoms. Hydrogen (H), along with nitrogen (N), oxygen (O), fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), exists as diatomic molecules (H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂) in its elemental form under standard conditions. Therefore, hydrogen is not monatomic.

50. Which one of the following is an example of physical change?

Which one of the following is an example of physical change?

Flowering of plants
Clotting of blood
Cooking of food
Melting of ice
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The correct answer is Melting of ice.
A physical change alters the form or appearance of a substance but not its chemical composition. It is often reversible. A chemical change results in the formation of new substances with different chemical properties.
Melting of ice is a change of state from solid water (ice) to liquid water. The chemical formula remains H₂O. This process is reversible (freezing). Flowering, clotting of blood, and cooking of food involve chemical reactions and the formation of new substances.
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