Chemistry MCQ Quiz - Objective Question with Answer for Chemistry - Download Free PDF

EXPLANATION:

• A. 50 g of H₂ (g):

  Number of moles = 50 g / 2 g/mol = 25 moles

  Number of molecules = 25 moles × 6.022 × 10²³ molecules/mol
  Number of atom= 2 x 25 moles × 6.022 × 1023 molecules/mol

• B. 44 g of CO₂ (g):

  Number of moles = 44 g / 44 g/mol = 1 mole

  Number of molecules = 1 mole × 6.022 × 10²³ molecules/mol
  Number of atom = 3 x 1 mole × 6.022 × 1023 molecules/mol

• C. 18 g of H₂O (l):

  Number of moles = 18 g / 18 g/mol = 1 mole

  Number of molecules = 1 mole × 6.022 × 10²³ molecules/mol
  Number of atom = 3 x 1 mole × 6.022 × 1023 molecules/mol

• D. 88 g of NH₃ (g):

  Number of moles = 88 g / 17 g/mol = 5.18 moles

  Number of molecules = 5.18 moles × 6.022 × 10²³ molecules/mol
  Number of atom = 4 x 5.18 moles × 6.022 × 10²³ molecules/mol

• E. 160 g of O₂ (g):

  Number of moles = 160 g / 32 g/mol = 5 moles

  Number of molecules = 5 moles × 6.022 × 10²³ molecules/mol
  Number of atoms = 2 x 5 moles × 6.022 × 10²³ molecules/mol

• Comparing the number of molecules for each, we see that:
  • B and C both have 1 mole of molecules.
  • Therefore, the correct answer is B and C only.

CONCEPT:

Type of Solutions and Their Examples

• A solution is a homogeneous mixture composed of a solute and solvent, which can be in different phases (solid, liquid, or gas).
• Gaseous solutions consist of gases dissolved in other gases, liquid solutions consist of liquids dissolved in other liquids, and solid solutions are solid mixtures.
• These solutions can be classified into gas-liquid, solid-liquid, and solid-solid solutions depending on the phase of the solute and solvent.

EXPLANATION:

• 1. Mixture of oxygen and nitrogen gases → Gaseous Solutions
  • This is a gaseous solution where oxygen and nitrogen gases mix homogeneously in the gas phase.
• 2. Ethanol dissolved in water → Liquid Solutions
  • Ethanol (a liquid) dissolves in water (a liquid), forming a liquid solution.
• 3. Solution of hydrogen in palladium → Solid Solutions
  • This is an example of a solid solution, where hydrogen gas dissolves in solid palladium, forming a homogeneous mixture in the solid phase.
• 4. Oxygen dissolved in water → Gas-Liquid Solutions
  • This is a gas-liquid solution, where oxygen (gas) dissolves in water (liquid), forming a homogeneous solution.
• 5. Copper dissolved in gold → Solid-Solid Solutions
  • Copper and gold are both solids, and when they mix to form an alloy, it is a solid-solid solution.
• The correct matching is as follows  1 - A, 2 - D, 3 - E, 4 - B, 5 - C

Therefore, the correct answer is: b) 1 - A, 2 - D, 3 - E, 4 - B, 5 - C

CONCEPT:

Ionization Constants of Acids

• The ionization constant (Kₐ) represents the equilibrium constant for the dissociation of an acid in water.
• For a polyprotic acid like acetic acid, the ionization occurs in steps, each with its own ionization constant (Kₐ₁, Kₐ₂, etc.).
• The overall ionization constant (K) is related to the individual Kₐ values, and the acid strength typically decreases with each successive ionization step.

EXPLANATION:

• Option A: log K = log Kₐ₁ + log Kₐ₂ is not correct. The overall ionization constant K is not simply the sum of the individual ionization constants in terms of logarithms. The correct relationship would be derived from the equilibrium expressions, but it does not follow the form of log K = log Kₐ₁ + log Kₐ₂.
• Option B: CH₃COOH is a stronger acid than CH₃COO⁻. This statement is true because acetic acid (CH₃COOH) is a weak acid and dissociates to form acetate ion (CH₃COO⁻). The conjugate base CH₃COO⁻ is much weaker than the parent acid CH₃COOH.
• Option C: Kₐ₁ > Kₐ₂ is true. In polyprotic acids like acetic acid, the first ionization constant (Kₐ₁) is always greater than the second (Kₐ₂), indicating that the first dissociation step is stronger than the second.
• Option D: Kₐ = (Kₐ₂ + Kₐ₁) / 2 is not correct. The overall ionization constant K is not the average of the individual Kₐ values, but rather it involves the product of the equilibrium concentrations derived from the individual dissociation steps.

Therefore, the correct answer is: B and C only.

CONCEPT:

Electronic Configuration of Transition Metals

• Transition metals are elements found in the d-block of the periodic table.
• These elements have partially filled d orbitals and typically show a variety of oxidation states.
• The electronic configuration of transition metals includes filling the 3d orbitals after the 4s orbitals.

EXPLANATION:

• Option A: [Ne]3s²3p⁶4s²3d⁶ is the electronic configuration of Iron (Fe), a transition metal, located in the d-block of the periodic table.
• Option B: [Ar]3d⁸4s² is the electronic configuration of Nickel (Ni), a transition metal, also found in the d-block.
• Option C: [Kr]4s²4d⁷5p³ is not a transition metal configuration. It corresponds to an element in the p-block (Arsenic, As), not a transition metal.
• Option D: [Xe]4f¹⁴5d⁷6s² is the electronic configuration of a lanthanide element (e.g., Dysprosium), not a transition metal, as it involves filling the 4f orbitals.

Therefore, the correct answer is: A and B only.

CONCEPT:

Energy Levels and Wavelengths in Hydrogen Atom

• Hydrogen atom transitions occur when an electron moves between quantized energy levels.
• The energy difference between levels is given by the formula:

  E = -13.6 × (1/n2final - 1/n2initial) eV

• The wavelength of the light absorbed or emitted during a transition is related to the energy difference:

  λ = hc/E

  Where h is Planck's constant, c is the speed of light, and E is the energy difference.

EXPLANATION:

• For the transition n = 2 → n = 3:
  • Energy difference:

    E1 = -13.6 × (1/32 - 1/22)

    E1 = -13.6 × (1/9 - 1/4) = -13.6 × (-5/36) = 13.6 × 5/36

  • Corresponding wavelength:

    λ1 = hc/E1

    λ1 is inversely proportional to E1.

• For the transition n = 4 → n = 5:
  • Energy difference:

    E2 = -13.6 × (1/52 - 1/42)

    E2 = -13.6 × (1/25 - 1/16) = -13.6 × (-9/) = 13.6 × 5/144

  • Corresponding wavelength:

    λ2 = hc/E2

    λ2 is inversely proportional to E2.

• Ratio of wavelengths:
  • λ1/λ2 = E2/E1
  • E1 = 13.6 × 5/36, E2 = 13.6 × 9/400
  • λ1/λ2 = (9/400) / (5/36) = 0.162 = 162/1000 = 81/500

Therefore, the ratio of the wavelengths is  81/500.

The correct answer is Antipyretic.

• Antipyretic is a drug that reduces fever.
  • Antipyretics cause the hypothalamus to override a prostaglandin-induced increase in temperature.
  • The body then works to lower the temperature, which results in a reduction in fever. 

Additional Information

• Barbiturates are a type of central nervous system (CNS) depressant used to treat insomnia, seizures, and headaches​.
• Antiseptic slows or stops the growth of micro-organisms on external surfaces of the body and helps to prevent infections.
• Antibiotics include a range of powerful drugs that kill bacteria or slow their growth. 
  • They treat bacterial infections. 

The correct answer is Na2CO3.

Key Points

• The sodium compound is used for softening hard water. Washing soda or sodium carbonate is used for removing the permanent hardness of the water.
• Washing soda has a chemical formula Na₂CO₃.10H2O.
• It binds calcium and magnesium molecules in water.
• Water can be softened by adding sodium carbonate (washing soda) or bypassing the water through an ion-exchange column.
• For large-scale municipal operations, a process known as the lime-soda process is used to remove Ca²⁺ and Mg²⁺ from the water supply.
•  

Additional Information

The correct answer is E.

Key Points

• Vitamin E is tocopherol.
• Vitamin E represents a group of compounds that contain both tocopherol and tocotrienol.
  • It is good for the immune system and it fights toxins.
  • It is a fat-soluble vitamin.
  • It is a very powerful antioxidant.
  • Weak muscles and fertility problems are signs of deficiency of vitamin E.
  • Its deficiency also causes hair damage and skin problems.

Important Points

Bleaching powder by its nature is an Oxidising agent.

• Stable bleaching powder is widely used as a disinfectant in water purification, as well as in the textile and pulp and paper industries.
• "Bleaching powder" is made by the action of chloride gas on calcium hydroxide.
• The reaction being essentially:
• 2Ca (OH)₂ + 2Cl₂ → Ca(OCl)₂ + CaCl₂ + 2H₂O.
• In the production of bleaching powder, slaked lime spread on the floors of large rectangular chambers of lead or concrete is exposed to chlorine gas.
• Bleaching powder, a solid combination of chlorine and slaked lime, was introduced in 1799 by Scottish chemist Charles Tennant.

The correct answer is Sugar in water.

Key Points

• The physical properties help in separating the homogenous mixtures.
• Those mixtures in which the substances are completely mixed together and are indistinguishable from one another are called homogeneous mixtures.
• A homogeneous mixture is a mixture in which the composition is uniform throughout the mixture.
• Many homogeneous mixtures are commonly referred to as solutions.
• Some of the examples of homogeneous mixtures (or solutions) are Sugar solution, Salt solution, Copper sulphate solution, Seawater, Alcohol and water mixture, Petrol and oil mixture, Soda water etc.

• Heterogeneous mixture:
  • A heterogeneous mixture is a mixture with a non-uniform composition that contains components in different phases.
  • The composition varies from one region to another with at least two phases that remain separate from each other, with clearly identifiable properties.
  • Heterogeneous mixtures contain particles that retain their chemical properties when they are mixed and can be distinguished after they are mixed.
  • The components of heterogeneous mixtures can be separated by the filtration of chemical procedures.
  • The two types of heterogeneous mixtures are suspensions and colloids.
  • Sugar and sand form a heterogeneous mixture. If you look closely, you can identify tiny sugar crystals and particles of sand.
  • Ice cubes in cola form a heterogeneous mixture.

The correct answer is A reducing agent.

Key Points

• Hydrogen peroxide H₂O₂ is acting as a reducing agent here.
• A reducing agent is a compound that oxidises itself and reduces the other compound in a chemical reaction.
• A reducing agent will lose electrons in a chemical reaction, and thus get oxidized.
• Here, the charge on Chlorine (Cl) is earlier 0, but after reaction, the charge on each Cl atom is -1, this shows that it has been reduced. Thus, Hydrogen peroxide has worked as a reducing agent.
• Also, in terms of hydrogen, adding hydrogen is termed as reduction, whereas removing it is termed as oxidation. Since hydrogen is added to chlorine, chlorine is reducing, and hence we can say that Hydrogen peroxide has worked as a reducing agent.

The correct answer is Increase.

Concept:

• Molarity:
  • It is defined as the moles of a solute per litres of a solution.
  • It is also known as the molar concentration of a solution.
• Molality:
  • It is defined as the number of moles of solute per kilogram of solvent.
• Mole fraction:
  • It is the ratio of moles of a component with the total moles of solute and solvent.
• Mass%:
  • It is the percentage of the mass of solute or solvent w.r.t total mass of solution.
• Formulas:

Explanation:

• Molarity depends on the volume of the solution.
• And volume is directly proportional to temperature.
• And when we increase the temperature the volume will increase.
• So the increase in volume leads to a decrease in Molarity as Molarity is inversely proportional to the volume of solution.

​Additional Information

Notes:

• Normality:
  • It is defined as the number of gram equivalent per litre of solution.
  • Also known as equivalent concentration.
  • Normality = Number of gram equivalents / [volume of solution in litres]
• Normality is inversely proportional to temperature.
• ​Volume is directly proportional to temperature.
• Molarity is inversely proportional to volume.
• Molarity is inversely proportional to temperature.
• Molality is not dependent on temperature.

The correct answer is Bauxite.Key Points

• Bauxite is an aluminium-rich sedimentary rock formed from laterite soil.
• It is found in tropical or subtropical regions.
• Bauxite is used for the production of Aluminium.
• Bauxite is a non-ferrous metallic mineral that is used in the manufacturing of aluminium.
• Bauxite is found mainly in tertiary deposits and is associated with laterite rocks.

 Important Points

• Odisha is the largest bauxite-producing state in India.
• More than half of India's bauxite deposits are found in Odisha.
• Bauxite is an important mineral used in the production of aluminium.

 Additional Information

Important ores:

The correct answer is Nitric acid.

• Nitric acid is used in the purification of gold and silver.

Key Points

• Nitric acid is used in the purification of gold. The acid mixture aqua regia, or royal water, dissolves gold and is used to purify scrap alloy containing gold.
  • Aqua regia is a mixture of hydrochloric acid and nitric acid in a 3:1 ratio.
  • Nitric acid is a nitrogen oxoacid of formula HNO3 in which the nitrogen atom is bonded to a hydroxy group and by equivalent bonds to the remaining two oxygen atoms.

Important Points

The correct answer is Uracil.

Key Points

• In DNA, Adenine, Guanine, Thymine, and Cytosine are present.
• In RNA Adenine, Guanine, Cytosine, and Uracil are present.
• Uracil
  • It is one of the four nucleobases in nucleic acid RNA.
  • In DNA, Uracil nucleobases are replaced by thymine.
  • Its formula is C₄H₄N₂O_2.

_{Additional Information}

•  Guanine
  • It is one of the four main nucleobases found in the nucleic acids DNA and RNA.
  • It is used to make one of the building blocks of DNA and RNA.
• Adenine
  • It is also one of the four main nucleobases found in the nucleic acids DNA and RNA.
  • It is part of many substances in the body that give energy to cells.
• Cytosine
  • It is pyrimidine and one of the nitrogenous bases found in RNA and DNA acid for making genetic code.
  • It Plays an essential role in forming base pairs by bonding with guanine.