Chemical Sciences MCQ Quiz - Objective Question with Answer for Chemical Sciences - Download Free PDF

Key Points

• During the electrolysis of brine (aqueous NaCl solution), NaOH, H₂, and Cl₂ are produced.
• Chlorine gas (Cl₂) is liberated at the anode (oxidation reaction).
• Hydrogen gas (H₂) is liberated at the cathode (reduction reaction).
• Sodium hydroxide (NaOH) is formed in the solution as a by-product.

Important Points

• Electrolysis of brine: Brine is a concentrated solution of sodium chloride (NaCl) in water. When subjected to electrolysis, it undergoes decomposition into its components.
• Chemical equation: 2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + H₂(g) + Cl₂(g).
• The process is widely used in the industrial production of chlorine, hydrogen, and sodium hydroxide.

The correct answer is Critical mass

Concept:-

• Nuclear Chain Reaction: Describes the process where one nuclear reaction triggers additional reactions, leading to a self-sustaining cascade.
• Critical Mass: The minimum amount of fissile material required for a sustained chain reaction.
• Neutron Moderation: Involves using materials to slow down fast neutrons, increasing their probability of causing fission reactions.
• Flux: Represents the rate of flow of neutrons, a critical parameter in achieving and maintaining criticality.

Explanation:-

Critical mass is the minimum amount of fissile material needed to sustain a self-sustaining nuclear chain reaction. It marks the point at which the rate of neutron production equals the rate of neutron loss.

Chain Reaction Fundamentals:

• A nuclear chain reaction involves the splitting (fission) of fissile nuclei, releasing energy and neutrons.
• Neutrons produced during fission can induce further fission reactions in neighboring fissile nuclei, creating a self-sustaining process.

Influence of Factors on Critical Mass:

• Factors affecting critical mass include fissile material purity, shape, density, and the presence of reflectors or moderators.
• Certain shapes and configurations can either increase or decrease the critical mass required.

Role of Flux and Neutron Moderation:

• Flux, representing the rate of neutron flow, is crucial for achieving and maintaining criticality.
• Neutron moderators, such as water or graphite, can slow down fast neutrons, making them more effective in causing fission reactions and reducing the critical mass.

Conclusion:-

So, The minimum amount of fissionable material that can produce a self sustaining chain reaction is called Critical mass

CONCEPT:

Principle of Preorganization in Supramolecular Chemistry

• The principle of preorganization refers to the idea that the host molecule in a supramolecular system is preorganized or pre-shaped to optimally bind to a guest molecule.
• This structural optimization of the host molecule enhances the stability and specificity of the host-guest complex by reducing the amount of conformational change needed during binding.
• By having a structure that is already well-suited to interact with the guest, the binding process becomes more efficient and leads to a more stable complex.

EXPLANATION:

• The correct answer is The principle that the host must be structurally optimized for binding before the complexation occurs
• Preorganization is a key concept in supramolecular chemistry, ensuring that the host molecule is geometrically and electronically ready to interact with the guest molecule.
• This principle reduces the entropic cost of binding and increases the overall stability and affinity of the supramolecular complex.

Reference: Preorganization involves the structural optimization of hosts for more stable binding with guests.

CONCEPT:

Comparative Synthesis and Selectivity of Cryptands and Crown Ethers

• Cryptands are a class of ligands known for their ability to form highly selective and stable complexes with cations by encapsulating them within a three-dimensional structure.
• While cryptands offer superior selectivity compared to crown ethers, they are generally more expensive and more challenging to synthesize due to their complex three-dimensional structures.
• Crown ethers, in comparison, are easier and less costly to produce but offer less selectivity when binding to cations.

EXPLANATION:

• The correct answer is Cryptands are more selective but more expensive and harder to synthesize than crown ethers
• Cryptands' superior selectivity arises from their ability to completely encapsulate cations, reducing interference from other ions.
• This benefit comes at the cost of increased difficulty in synthesis and higher expense relative to crown ethers.

Reference: Cryptands offer better selectivity but are more expensive and difficult to synthesize.

CONCEPT:

Discovery of Crown Ethers

• Crown ethers are a class of cyclic chemical compounds that consist of a ring containing several ether groups.
• These compounds were discovered by Charles J. Pedersen, who was awarded the Nobel Prize in Chemistry in 1987 for this work.
• The phrase "chance favors the prepared mind" is famously associated with Pedersen's discovery, highlighting the role of prepared scientific intuition in making groundbreaking discoveries.

EXPLANATION:

• The correct answer is Crown ethers
• Charles J. Pedersen's discovery of crown ethers was significantly influenced by his readiness to recognize and investigate unexpected results, exemplified by the phrase "chance favors the prepared mind."
• Crown ethers have the ability to form stable complexes with cations, making them important in various applications including phase transfer catalysis and ion transport.

Reference: This phrase is connected to the discovery of crown ethers by Charles J. Pedersen.

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.

• The properties of the ionic compounds include:-
• Solid structure and hard surface
• High Melting and boiling points
• Solubility in water
• The ionic compounds have high melting and boiling points due to the strong forces of attraction present between the particles of the compound.
• The ionic bonding grants strength to the structure.
• Thus, Low melting and boiling points are not the property of an ionic compound.

Key Points

• The s-block element that is a silvery- metal and is used in an alloy with copper or nickel to make various equipment is Beryllium.
• Beryllium is a lightweight and strong metal that is widely used in aerospace, defense, and nuclear industries.
• It has a high melting point, good thermal conductivity, and is also a good electrical conductor.
• Atomic number of Beryllium is - 4.

Additional Information

• Rubidium is a soft, silvery- metal that is highly reactive.
  • It is used in atomic clocks and as a catalyst in certain chemical reactions.
• Francium is a highly radioactive and unstable element.
  • It is extremely rare and has no practical applications.
• Caesium is a soft, silvery-golden metal that is also highly reactive.
  • It is used in atomic clocks, drilling fluids, and in the treatment of cancer.

Concept:

Median

Case 1: If number of observation (n) is even

\({\rm{Median\;}} = {\rm{\;}}\frac{{{\rm{value\;of\;}}{{\left( {\frac{{\rm{n}}}{2}} \right)}^{{\rm{th}}}}{\rm{\;observation\;}} + {\rm{\;\;value\;of\;}}{{\left( {\frac{{\rm{n}}}{2}{\rm{\;}} + 1} \right)}^{{\rm{th}}}}{\rm{\;observation}}}}{2}\)

Case 2: If number of observation (n) is odd

\({\rm{Median\;}} = {\rm{value\;of\;}}{\left( {\frac{{{\rm{n}} + 1}}{2}} \right)^{{\rm{th}}}}{\rm{\;observation}}\)

Calculation:

Arrange the observations in the ascending order are

1, 2, 3, 6, 8, 9

Here, n = 6 = even.

So, 3^rd and 4^th observation are 3 and 6

∴\({\rm{Median}} = {\rm{\;}}\frac{{3 + 6}}{2} = 4.5\)

The correct answer is NH₃ and HCl

Key Points

• Dalton's law is applicable only to a mixture of non-reacting gases.
• Ammonia (NH₃) reacts with hydrochloric acid at normal temperature and gives ammonium chloride(NH₄Cl).
• NH₃ + HCl    →    NH₄Cl
• So, this gaseous mixture does not follow Dalton's law.

Additional Information

Dalton's law:

• Dalton's law states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.
• This empirical law was observed by John Dalton in 1801.
• It was published in 1802.
• It is also called Dalton's law of partial pressures.
• Dalton's law is related to the ideal gas laws.
• Dalton's law is not strictly followed by real gases, with the deviation increasing with pressure.

Important Points

• Helium is a noble gas that will not react with hydrogen gas, so this gaseous mixture follows Dalton’s law.
• Nitrogen gas is not reactive in normal temperatures because the breakdown of nitrogen into atomic form is a highly endothermic process.
• Nitrogen and oxygen gas are not found in their atomic form in normal temperatures, so these gases will not react with each other. 

Explanation:- 

• Allotropes of carbon like Diamond, Graphite, and Fullerene show crystalline structures.
• Fullerene has infinite lattices of Diamond and Graphite.
• It is formed by nanotubes forming the discrete molecular structure.

Additional Information 

• Fullerene molecule consists of carbon atoms connected by single and double bonds.
• Common structures are C₆₀ and C_70.

The correct answer is S > Se > O

Concept:

• The amount of energy released when an extra electron is added to a neutral atom to form a ​negatively charged ion is called electron affinity.
• Since energy is released, it is represented with negative sign.

​               \(A+ e^- \rightarrow A^- \)    .... \(\Delta _{aff}H = -ive \)

• Atoms with high electron affinity have higher tendency to accept the electron.
• Electron affinity depends on Nuclear Charge, Atomic size as well as the electron distribution in orbitals.

Explanation:

• Down the group, new shell is added. The size of atom increases and therefore, the attraction between nucleus and outermost electron decreases which further decreases the electron affinity.
• Hence  K > Li > Na is incorrect as K is the largest among three elements
• The small atoms cannot accommodate incoming electron and undergo inter-electronic repulsions. Thus, First element of the group will have least electron affinity for one-electron gain.

Thus, F > Cl > Br and P > N > As are incorrect as F and N being smallest element should have least electron affinity.

Conclusion:

Hence, the correct  order of electron affinity for one-electron gain is: S > Se > O

13, 8, 15, 14, 17, 9, 14, 16, 13, 17, 14, 15, 16, 15, 14

First of all, we arrange the data in ascending order, then

8, 9, 13, 13, 14, 14, 14, 14, 15, 15, 15, 16, 16, 17, 17

Total number (n) = 15

As we know,

Median = [(n + 1)/2]^th = [(15 + 1)/2]^th = [16/2]^th = 8^th number

8^th number is 14

So, x = 14

If 8 is replaced by 18 then,

13, 18, 15, 14, 17, 9, 14, 16, 13, 17, 14, 15, 16, 15, 14

Again, we arrange the data in ascending order, then

9, 13, 13, 14, 14, 14, 14, 15, 15, 15, 16, 16, 17, 17, 18

Total number (n) = 15

Median = [(n + 1)/2]^th = [(15 + 1)/2]^th = [16/2]^th = 8^th number

8^th number is 15

So, y = 14

x + y

⇒ 14 + 15

Concept:

Explanation:

• Option (1) is incorrect because ricin is a toxin obtained from Ricinus plant.
• Vinblastin and curcumin are drugs.
• Morphine and codeine are alkaloids.
• Abrin is also a toxin obtained by the plant Abrus.
• Concanavalin A is a lectin.​

The correct answer is - 3) Protein

Concept:

Fat -

• Fats are a type of lipid consisting of triesters of glycerol and fatty acids or triglycerides. 

Carbohydrates -

• Carbohydrates are defined as “optically active polyhydroxy aldehydes or ketones or the compounds which produce units of such type on hydrolysis”. 

Protein - 

• A protein is a naturally occurring, extremely complex substance that consists of amino acid residues joined by peptide bonds.

Nucleic Acid - 

• Nucleic acids are polynucleotides that are, long chainlike molecules composed of a series of nearly identical building blocks called nucleotides.
• Each nucleotide consists of a nitrogen-containing aromatic base attached to a pentose (five-carbon) sugar, which is in turn attached to a phosphate group

Explanation:

Biuret test - The biuret test is a chemical test that can be used to check for the presence of peptide bonds in a given analyte.

• Therefore, the biuret test can also be used to gauge the amount of protein present in the analyte.
• In this test, the presence of peptides results in the formation of pale purple-coloured coordination compounds of the copper (II) ion (when the solution is sufficiently alkaline). 
• The copper (II) present in the reaction binds itself to the nitrogen atoms that are present in the protein peptides. 

Therefore, the Biuret test is used to test the presence of Protein.