Practice Test - NEET MCQ

According to recent researches the magnetic field of earth is considered due to a large bar magnet situated in earth's core.
It is considered that the north pole of this large magnet is situated at the geographical south of earth and vice versa and as the magnetic field due to a bar magnet is from north pole to south pole of the maget thus the earth's magnetic field is considered from geographical south to geographical north which are respectively north and south poles of the bar magnet.

B=B₀+Bm
= μ₀nI+ μmnI
=nI(μ+ μm)
=60x5(5000μ₀+ μ₀)
B=300(5001μ₀)
B=1.88T
H=B/μm
=300x5001μ₀/5000μ
=300AT

Work required to turn the dipole is given by
W=MB[cosθ_i- cosθ_f]
Here θi is the initial angle made by a dipole with a magnetic field and   is the final angle made by a dipole with a magnetic field.
magnetic moment is normal to the field direction.
so, θ_i=0 and θ_f=90
W = 1.5 × 0.22 [ cos0° - cos90° ]
W = 0.33J
 
magnetic moment is opposite to the field direction.
so, θ_i=0 and θ_f=180
now, W = 1.5 × 0.22 [ cos0° - cos180°]
= 0.33 [ 1 - (-1) ]
= 0.66 J

The earth's magnetic field is Be​ and its horizontal and vertical components are H_e​ and H_v​
cosθ= H_e​​/B_e​
∴cos60^o= (​0.26×10^−4​/ B_e )T
⇒B_e​=(​0.26×10⁻⁴)/ (½)​=0.52×10⁻⁴T=0.52G

All substances show some kind of magnetic behaviour. After all, they are made up of charged particles: electrons and protons. It is the way in which electron clouds arrange themselves in atoms and how groups of these atoms behave that determines the magnetic properties of the material. The atom (or group of atoms) in effect becomes a magnetic dipole or a mini bar magnet that can align according to the magnetic field applied. The net effect of all these dipoles determines the magnetic properties of the Magnetic Materials.

 =1.5x0.22
 =15x22x10-3
 =330x10-3
Τ=0.33J
 

• For all spontaneous chemical reactions, the change in Gibbs free energy (ΔG°) is always negative.
• For a spontaneous reaction in an electrolytic cell, the cell potential (E°cell) should be positive.

In an electrochemical cell, when an opposing externally potential is applied and increased slowly, the reaction continues to take place.

• When the external potential is equal to the potential of the cell, the reaction stops.
• Once the externally applied potential is greater than the potential of the cell, the reaction goes in the opposite direction and the cell behaves like an electrolytic cell.

The correct order of equivalent conductance at infinite dilution is KCl > NaCl > LiCl.

Anion is same (chloride ion) for all the species. Larger is the size of the cation, greater is the equivalent conductance at infinite dilution and vice versa.

Explanation for the Use of Saturated KNO₃ Solution for Salt-Bridge

• The primary purpose of a salt bridge is to maintain electrical neutrality within the internal circuit of an electrochemical cell. It allows the migration of ions to balance the charge during the redox reactions.
• A saturated solution of KNO₃ is often used to make a salt bridge because of the similar velocities of K⁺ (potassium ions) and NO^3- (nitrate ions) which helps maintain electrical neutrality in the cell, and prevents cell polarization.

Specific conductance = Cell constant/Resistance
∴ Specific conductance ∝ 1/Resistance 
∴ The one with the lowest resistance (order 10^-9) will have the highest specific conductance.
Hence, option A is correct.

Flow of Electrons in an Electrolytic Cell
In an electrolytic cell, the flow of electrons is from: Anode to Cathode through Internal Supply
This means that option B is correct. Here's why:

• Anode: This is where oxidation takes place in an electrolytic cell. During oxidation, a substance loses electrons. This means that the anode is the source of electrons.
• Cathode: This is where reduction takes place in an electrolytic cell. During reduction, a substance gains electrons, meaning that the cathode is where electrons are received.
• Flow of electrons: Since electrons are produced at the anode (through oxidation) and consumed at the cathode (through reduction), the flow of electrons is from the anode to the cathode.
• Internal supply: In an electrolytic cell, the power supply is connected to the anode and cathode, creating an electric current within the cell. This current forces the electrons to move from the anode to the cathode, hence the term "through internal supply".

In summary, in an electrolytic cell, the flow of electrons is from anode to cathode through internal supply as a result of the oxidation and reduction reactions taking place at the anode and cathode, respectively.

Fe²⁺ +2e⁻→Fe, E^o = −0.440 ......(1)
Fe³⁺ + 3e⁻ → Fe, E^o = −0.036.......(2)
The standard electrode potential for Fe³⁺ +e⁻ →Fe²⁺ is obtained by substracting the value of the standard electrode potential for first reaction from the standard electrode potential for second reaction. 
−0.036 −(−0.440) = 0.404V

• Plasmids renature because they have supercoiled structures that have held the two strands of the helix together during denaturation.
• Chromosomal DNA is not able to renature, however, because its longer strands have become mixed with denatured proteins.

• Insertional inactivation is the inactivation of a gene upon insertion of another gene inside in its place or within its coding sequence.
• It help in identification of recombinant clones.

• Having two antibiotic resistance genes in the same plasmid helps in identifying transformants.
• Transformants take up the plasmid and also integrate it into recombinant DNA.

• The polymerase chain reaction is a technology in molecular biology used to amplify a single copy or a few copies of a piece of DNA.
• Calcium ions is not required in PCR technology.

In agarose gel electrophoresis, the DNA fragments separate out (resolve) according to their size or length because of the sieving property of agarose gel. It means, the smaller the fragment size, the farther it will move.

Restriction enzymes are also called 'molecular scissors' as they cleave DNA at or near specific recognition sequences known as restriction sites. These enzymes make one incision on each of the two strands of DNA and are also called restriction endonucleases.

• All the enzymes at higher temperature become inactive.
• Denaturation is done at high temperature as it leads to breaking down of hydrogen bonds between the bases of polynucleotides.

• Origin of replication is the specific DNA sequence on chromosome that which is responsible for initiating replication.
• Origin of replication is essential for replication of particular DNA segment.

The groups of letters that form same words when read both forward and backward are called Palindrome. For example MALYALAM which read same from both side.

Recombinant DNA is a form of DNA whose nucleotide sequence has undergone alteration as a result of incorporation of exchange with another DNA strand. In recombinant DNA technology, human genes are often transferred into bacteria or yeast because both bacteria and yeast multiply very fast to form huge population, which expresses the desired gene. By doing so, one can observe the phenotypes of the gene more quickly and in a larger scale than by studying the same traist in humans.

DNA fingerprinting technique in which the banding pattern of DNA fragments is compared and can be used in many species, including the human, to indicate relatedness. DNA is digested with restriction enzymes, run on an electrophoretic gel, and blots made from the gel. Such blots are then hybridized with radiolabelled probe DNA consisting of cloned sequences of the short interspersed repeat sequences which are common in vertebrate genomes. Autoradiography provides a distinct banding pattern of DNA fragments containing such DNA sequences.

A represents polypeptide chain C which is removed prior to insulin formation

Using conventional methods of diagnosis (serum and urine analysis, etc.) early detection is not possible. Recombinant DNA technology, Polymerase Chain Reaction (PCR) and Enzyme Linked Immuno-sorbent Assay (ELISA) are some of the techniques that serve the purpose of early diagnosis.

A single stranded DNA or RNA joined with a radioactive molecule (probe) is allowed to hybridise to its complementary DNA in a clone of cells. It is followed by detection using autoradiography. The clone having the mutated gene will not appear on the photographic film, because the probe will not have the complementarity with the mutated gene. 

Gene therapy is a newly emerging branch of biotechnology with tremendous results. It is basically used for correcting genetic disorders. In gene therapy, normal genes are introduced in the cells to replace the missing genes or defective genes. 
Early gene therapy has been proved to be more effective in treating certain brain diseases in humans. They have also shown exemplary results in mice.  
When a child is born, he has its innate immunity, which does not allow any foreign body to settle into its own body easily. But before birth, it has not yet recognized itself, so therapy would be easily accepted.