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

CONCEPT:

Iodoform Reaction

• The iodoform reaction is a chemical reaction in which a compound containing a methyl group (CH3) attached to a carbonyl group (C=O), like methyl ketones, reacts with iodine in the presence of a base to form iodoform (CHI3).
• Compounds that typically give the iodoform reaction include methyl ketones (RCOCH3) and alcohols that have a methyl group (CH3) attached to a carbonyl group.
• Examples of compounds that will NOT give the iodoform reaction are aldehydes and ketones that do not have the CH3 group attached to the carbonyl carbon.

EXPLANATION:

Compound	Structure	Iodoform Test
Ethanol		Positive
Isopropyl alcohol		Positive
Bromoacetone		Positive
2-Butanol		Negative
2-Butanone		Positive
Butanal		Negative
2-Pentanone		Positive
3-Pentanone		Positive
Pentanal		Negative
3-Pentanol		Negative

• The following compounds will not give the iodoform reaction:
  • Butanal: Aldehydes do not generally give the iodoform reaction unless they have a methyl group adjacent to the carbonyl group.
  • 2-Pentanone: Ketones without a methyl group adjacent to the carbonyl group do not undergo the iodoform reaction.
  • Pentanal: Similar to butanal, this is an aldehyde and does not contain the necessary CH3 group next to the carbonyl group.
  • 3-Pentanol: Although it is an alcohol, it does not contain a methyl group adjacent to the carbonyl group, which is necessary for the iodoform reaction.
• Thus, the number of molecules that will not give the iodoform reaction is 4, corresponding to butanal, 2-pentanone, pentanal, and 3-pentanol.

Therefore, the correct answer is 4.

CONCEPT:

VSEPR Theory – Electron Domains and Molecular Geometry

• The VSEPR (Valence Shell Electron Pair Repulsion) theory helps predict molecular shapes based on repulsion between electron domains (bonding + lone pairs) around the central atom.
• Electron geometry is determined by the total number of electron domains.
• Molecular geometry depends on how many of these are bonding pairs vs lone pairs.

EXPLANATION:

• The given molecule is PQ₄R, where:
  • P is the central atom and the least electronegative.
  • Q is a halogen (all four Q atoms are identical).
  • R is the most electronegative element (likely fluorine).
• P is bonded to:
  • 4 Q atoms (4 bonding pairs)
  • 1 R atom (1 bonding pair)
  • 1 lone pair
• Total electron domains = 5 bonding pairs + 1 lone pair = 6 electron domains
• Electron geometry for 6 domains → Octahedral
• With 1 lone pair:
  • The lone pair occupies one position.
  • The 5 remaining bonding atoms form a square pyramidal geometry.

Therefore, the correct molecular geometry is: Square pyramidal.

CONCEPT:

Carbocation Stability and Rate of Hydrolysis

• During hydrolysis of alkyl halides, the leaving group (e.g., Br⁻) departs, forming a carbocation intermediate.
• The rate of hydrolysis depends on the stability of this carbocation: more stable carbocation = faster reaction.
• Carbocation stability is enhanced by:
  • Aromaticity (most stabilizing)
  • +R (resonance) effect from groups like phenyl rings
  • +I (inductive) effect from alkyl groups like methyl

EXPLANATION:

• Compound III: Forms a carbocation that is homoaromatic, fulfilling Hückel’s rule with delocalized electrons. This offers the greatest stability due to aromaticity.
• Compound II: The carbocation is stabilized by resonance with three phenyl groups (+R effect), making it highly stable.
• Compound IV: Stabilized by +I effect of three methyl groups; less effective than resonance or aromaticity.
• Compound I: The carbocation is at a bridgehead position, violating Bredt’s rule, making it extremely unstable.

• Order of stability of carbocations: III > II > IV > I
• Since rate of hydrolysis ∝ stability of carbocation:

Correct rate of hydrolysis order: III > II > IV > I

Therefore, the correct answer is: Option II (III > II > IV > I).

CONCEPT:

Stability of Carbon Radicals

• The stability of carbon radicals depends on factors like:
  • Hybridization of the carbon (sp < sp² < sp³)
  • Resonance stabilization
  • Hyperconjugation and inductive effects
• More resonance structures and hyperconjugation from adjacent alkyl groups increase radical stability.
• Radicals on sp-hybridized carbon atoms are the least stable due to high s-character.

EXPLANATION:

• We are asked to identify the most stable and least stable carbon radicals from homolytic cleavage of the C–H bonds in structure (X).
• Structure III has 5 alpha hydrogens and is resonance stabilized due to the presence of a carbonyl group, making its radical the most stable.
• Structure II forms a radical on an sp-hybridized carbon, which is inherently unstable due to high s-character and lack of resonance stabilization.
• Hence, III is the most stable and II is the least stable radical.

Therefore, the correct answer is: Option IV (III and II).

CONCEPT:

Qualitative Inorganic Analysis - Group Reactions

• In qualitative inorganic analysis, cations are grouped based on their reactions with specific reagents.
• The reagents used for cation analysis include H₂S, NH₄OH, and (NH₄)₂CO₃, which help in identifying different metal ions by forming precipitates or dissolving in certain conditions.

EXPLANATION:

• For Cations (P) Pb²⁺, Cu²⁺: These cations are in Group II, where they react with H₂S in the presence of dilute HCl, forming black precipitates of metal sulfides.
  • Correct Group Reagent: (i) H₂S in the presence of dilute HCl.
• For Cations (Q) Al³⁺, Fe³⁺: These cations belong to Group III, and they react with NH₄OH in the presence of NH₄Cl, forming hydroxide precipitates.
  • Correct Group Reagent: (iii) NH₄OH in the presence of NH₄Cl.
• For Cations (R) Co²⁺, Ni²⁺: These cations are in Group IV, where they react with H₂S in the presence of NH₄OH, forming black or dark-colored sulfide precipitates.
  • Correct Group Reagent: (iv) H₂S in the presence of NH₄OH.
• For Cations (S) Ba²⁺, Ca²⁺: These cations belong to Group V, and they react with (NH₄)₂CO₃ in the presence of NH₄OH, forming white precipitates of carbonates.
  • Correct Group Reagent: (v) (NH₄)₂CO₃ in the presence of NH₄OH.

Therefore, the correct matching is P → (i), Q → (iii), R → (iv), S → (v)

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.