BASIC CONCEPTS OF CHEMISTRY

BASIC CONCEPTS OF CHEMISTRY

1. The force of attraction between the particles of matter is maximum in:

• Options:
  A) Alcohol
  B) Water
  C) Air
  D) Copper
• Answer: D) Copper
• Explanation: In solids like copper, particles are tightly packed with strong intermolecular forces of attraction. This is why solids retain a fixed shape and volume.

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2. Which of the following statements is not correct regarding matter?

• Options:
  A) Matter is made up of particles.
  B) There is a force of attraction between particles of matter.
  C) There is no attraction force between particles of matter.
  D) The particles of matter are usually in motion and move continuously.
• Answer: C) There is no attraction force between particles of matter.
• Explanation: Matter always has some force of attraction between particles, though it varies depending on the state (solid, liquid, or gas).

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3. Density of water is:

• Options:
  A) 500 kg/m³
  B) 1000 kg/m³
  C) 1500 kg/m³
  D) 2000 kg/m³
• Answer: B) 1000 kg/m³
• Explanation: The standard density of water is 1000 kg/m³ at 4°C.

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4. In ionic compounds, ions attract each other and are held together by a strong:

• Options:
  A) Electrostatic forces
  B) Magnetic forces
  C) Gravitational forces
  D) Electric forces
• Answer: A) Electrostatic forces
• Explanation: Ionic compounds are held together by strong electrostatic forces of attraction between positively and negatively charged ions.

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5. The number of moles present in 90 g of water is:

• Options:
  A) 4
  B) 5
  C) 6
  D) 7
• Answer: B) 5
• Explanation:
  Moles = Mass / Molar mass = $\frac{90}{18} = 5$ moles.
  The molar mass of water (H₂O) is 18 g/mol.

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6. Which of the following is a physical change?

• Options:
  A) Melting of ice
  B) Milk turning into curd
  C) Ripening of fruits
  D) Grapes getting fermented
• Answer: A) Melting of ice
• Explanation: Melting of ice is a physical change because it involves a change of state without altering the chemical composition of water.

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7. What is the purity of sterling silver?

• Options:
  A) 916
  B) 925
  C) 935
  D) 950
• Answer: B) 925
• Explanation: Sterling silver is 92.5% pure silver, with 7.5% made up of other metals, usually copper.

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8. The relative mass of CO is:

• Options:
  A) 28
  B) 44
  C) 12
  D) 16
• Answer: A) 28
• Explanation:
  The molar mass of carbon monoxide (CO) = $12 + 16 = 28$ g/mol.

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9. What is the number of particles present in 1 mole of any substance?

• Options:
  A) $6.022 \times 10^{23}$
  B) $6.023 \times 10^{22}$
  C) $6.023 \times 10^{24}$
  D) $6.022 \times 10^{22}$
• Answer: A) $6.022 \times 10^{23}$
• Explanation: This is Avogadro's number, representing the number of particles in one mole of a substance.

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10. Which of the following methods can be used for separating a mixture of NaCl and NH₄Cl?

• Options:
  A) Crystallization
  B) Centrifugation
  C) Chromatography
  D) Sublimation
• Answer: D) Sublimation
• Explanation: NH₄Cl sublimates (turns directly into vapor) on heating, leaving NaCl behind.

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11. ____is the heat per unit mass required to change a substance from solid into liquid at the same temperature:**

• Answer: Latent heat of fusion
• Explanation: This is the energy needed to overcome intermolecular forces during a phase change from solid to liquid.

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12. Molarity is:

• Options:
  A) The number of moles of solute in 1 liter of solvent
  B) The number of moles of solute in 1 kilogram of solvent
  C) The number of moles of solute in 1 liter of solution
  D) The number of moles of solute in 1 kilogram of solution
• Answer: C) The number of moles of solute in 1 liter of solution
• Explanation: Molarity (M) = $\frac{\text{moles of solute}}{\text{volume of solution (in liters)}}$.

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13. Which scientist provided the basic theory about the nature of matter?

• Options:
  A) Democritus
  B) Joseph Proust
  C) John Dalton
  D) Antoine Lavoisier
• Answer: C) John Dalton
• Explanation: Dalton proposed the atomic theory, which states that matter is composed of indivisible atoms.

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14. In CaO, the ratio of Ca and O by mass is:

• Options:
  A) 5:2
  B) 3:8
  C) 2:5
  D) 8:3
• Answer: A) 5:2
• Explanation: The molar mass of Ca = 40 g/mol, and O = 16 g/mol. So, $\text{Mass ratio} = \frac{40}{16} = 5:2$.

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15. In general, the physical classification of states of matter does not include the____ state

Options:
A) Colloidal
B) Gaseous
C) Liquid
D) Solid

Correct Answer: A) Colloidal
Explanation:
The physical classification of matter traditionally includes solid, liquid, and gaseous states. Colloidal is not considered a distinct physical state of matter; instead, it is a heterogeneous mixture where particles are dispersed in another medium.

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16. Which of the following statements is/are true?

A: Rigidity is the property of matter to maintain its shape even if external force works on it, and solids show this property.
B: Fluidity is the property of a substance to flow easily and allow changes in its shape under external forces, exhibited by liquids and gases.

Options:
A) Only A is true
B) Only B is true
C) A and B both are false
D) A and B both are true

Correct Answer: D) A and B both are true
Explanation:

• Rigidity is a characteristic property of solids that maintain their shape even under external forces.
• Fluidity is a property of liquids and gases that allows them to flow and take the shape of their container.

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17. Which state of matter is obtained by cooling a gas of very low density to extremely low temperatures?

Options:
A) Gas
B) Plasma
C) Bose-Einstein Condensate (BEC)
D) Plasma Condensate

Correct Answer: C) Bose-Einstein Condensate (BEC)
Explanation:
BEC is a state of matter formed at temperatures close to absolute zero, where particles behave as a single quantum entity. It is distinct from solids, liquids, gases, or plasma.

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18. _____________On mixing with water changes to gypsum.

Options:
A) Calcium Phosphate
B) Sodium Hydrogen Carbonate
C) Calcium Sulphate Hemihydrate
D) None of these

Correct Answer: C) Calcium Sulphate Hemihydrate
Explanation:
Calcium sulfate hemihydrate (CaSO₄·0.5H₂O), also known as Plaster of Paris, reacts with water to form gypsum (CaSO₄·2H₂O).

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19. Using which of the following processes can one separate a solute from its solution?

Options:
A) Sedimentation
B) Evaporation
C) Filtration
D) Condensation

Correct Answer: B) Evaporation
Explanation:
Evaporation is the process used to separate a solute (e.g., salt) from a solution by heating it until the solvent (e.g., water) evaporates, leaving the solute behind.

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20. Which element is added to hydrocarbons in a more rapid reaction in the presence of sunlight?

Options:
A) Oxygen (O)
B) Nitrogen (N)
C) Hydrogen (H₂)
D) Chlorine (Cl₂)

Correct Answer: D) Chlorine (Cl₂)
Explanation:
Chlorine reacts with hydrocarbons in a photochemical reaction under sunlight to form chlorinated hydrocarbons. This reaction involves free radical substitution.

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21. Multi-use plastic water bottles are made of

Options:
A) Bakelite
B) Polystyrene
C) Polyethylene
D) Silicon

Correct Answer: C) Polyethylene
Explanation:
Polyethylene is a durable, lightweight, and flexible plastic commonly used for making reusable water bottles.

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22. What is the approximate molecular weight of common salt?

Correct Answer: 58.44 g/mol
Explanation:
Common salt, or sodium chloride (NaCl), has a molecular weight calculated as:

• Sodium (Na): 22.99 g/mol
• Chlorine (Cl): 35.45 g/mol
  Total = 22.99 + 35.45 = 58.44 g/mol

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23. Turpentine oil can be purified by

Options:
A) Steam distillation
B) Simple distillation
C) Fractional distillation
D) Vacuum distillation

Correct Answer: A) Steam distillation
Explanation:
Turpentine oil contains components that are sensitive to high temperatures. Steam distillation is used because it purifies the oil without decomposing it, as it operates at lower temperatures compared to simple or vacuum distillation.

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24. The boiling point of water is

Options:
A) 50°C
B) 0°C
C) 100°C
D) 10°C

Correct Answer: C) 100°C
Explanation:
At standard atmospheric pressure, water boils at 100°C. This is a fundamental property of water.

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25. In CO₂, C and O are present in the ratio by mass

Options:
A) 1:8
B) 8:1
C) 8:3
D) 3:8

Correct Answer: A) 1:8
Explanation:
The molar mass of CO₂ is 44 g/mol (C = 12, O₂ = 32). The ratio of carbon to oxygen by mass is $\frac{12}{32} = 1:8$.

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26. How many moles are present in 54 g of He?

Options:
A) 13.5 moles
B) 10 moles
C) 1.12 moles
D) 25 moles

Correct Answer: B) 13.5 moles
Explanation:
The molar mass of helium (He) is 4 g/mol.

$$\text{Number of moles} = \frac{\text{mass}}{\text{molar mass}} = \frac{54}{4} = 13.5$$

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27. How can one state of matter be changed into another?

Options:
A) By absorbing or radiating heat energy
B) By increasing pressure
C) By using electrolytes
D) By using acids and bases

Correct Answer: A) By absorbing or radiating heat energy
Explanation:
States of matter can change by heating (e.g., ice melting to water) or cooling (e.g., water freezing to ice). Pressure also influences these changes, but heat is the primary factor.

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28. What are the brief bursts of energy arising from the sun's photosphere?

Options:
A) Solar energy
B) Solar flares
C) Sunspots
D) Solar wind

Correct Answer: B) Solar flares
Explanation:
Solar flares are sudden, intense bursts of radiation from the sun's photosphere, releasing energy in various forms like light and heat.

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29. Which of the following allotropes of carbon is a good conductor of electricity?

Options:
A) Charcoal
B) Diamond
C) Graphite
D) Fullerene

Correct Answer: C) Graphite
Explanation:
Graphite has free electrons that allow it to conduct electricity. Other allotropes, like diamond, lack this property.

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30. The melting point of ice is

Options:
A) 273 K
B) 273°C
C) 0°C
D) -273 K

Correct Answer: A) 273 K
Explanation:
The melting point of ice is 0°C, which equals 273 K (Kelvin scale).

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31. A substance that cannot be broken down into simpler substances is called

Options:
A) Element
B) Compound
C) Heterogeneous mixture
D) Homogeneous mixture

Correct Answer: A) Element
Explanation:
An element is the simplest form of matter and cannot be decomposed into simpler substances chemically (e.g., hydrogen, oxygen).

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32. Water can exist in three states of matter.

Statements:
A) Solid, as ice
B) Liquid, as petrol
C) Gas, as oxygen

Options:
A) Only A is true
B) A and B are true; C is false
C) All are false
D) All are true

Correct Answer: A) Only A is true
Explanation:
Water exists in three states: ice (solid), liquid water, and water vapor (gas). Petrol is not a state of water, and oxygen is not water in any form.

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33. Presently, scientists are talking of how many states of matter?

Options:
A) 3
B) 2
C) 4
D) 5

Correct Answer: D) 5
Explanation:
The five states of matter are solid, liquid, gas, plasma, and Bose-Einstein condensate (BEC).

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34. The percentage of water of crystallization in washing soda is

Options:
A) 10.6%
B) 37.06%
C) 62.9%
D) 70.06%

Correct Answer: C) 62.9%
Explanation:
Washing soda (Na₂CO₃·10H₂O) contains 10 water molecules as part of its crystalline structure. The percentage is calculated as:

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35. What is the molecular mass of ozone?

Options:
A) 32 u
B) 48 u
C) 84 u
D) 160 u

Correct Answer: B) 48 u
Explanation:
Ozone (O₃) consists of three oxygen atoms. Each oxygen atom has a mass of 16 u.

$$\text{Molecular mass} = 3 \times 16 = 48 \, \text{u}$$

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36. Which of the following scientists worked on the fifth state of matter?

Options:
A) C.V. Raman
B) Vikram Sarabhai
C) Satyendra Nath Bose
D) Homi Bhabha

Correct Answer: C) Satyendra Nath Bose
Explanation:
Satyendra Nath Bose collaborated with Albert Einstein to predict the Bose-Einstein Condensate, the fifth state of matter.

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37. In pure water, the concentrations of H⁺ ions and OH⁻ ions are

Options:
A) Equal
B) Unequal
C) OH⁻ ions are more
D) H⁺ ions are more

Correct Answer: A) Equal
Explanation:
In pure water, the concentration of H⁺ ions and OH⁻ ions is equal at $1 \times 10^{-7}\, \text{mol/L}$, making it neutral.

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38. A molecule of any substance contains $6.023 \times 10^{23}$ particles. If $3.05 \times 10^{23}$ particles are present in CO₂, the number of moles is

Options:
A) 0.25
B) 0.5
C) 1
D) 2

Correct Answer: B) 0.5
Explanation:

$$\text{Number of moles} = \frac{\text{Number of particles}}{\text{Avogadro's number}} = \frac{3.05 \times 10^{23}}{6.023 \times 10^{23}} = 0.5$$