All questions of August Week 2 for NEET Exam

Just electronegativity matters

When Cl2 reacts with hot and concentrated NaOH, then....6NaOH+3Cl2→5NaCl +NaClO3+3H2O...When Cl2 reacts with cold and dilute NaOH then ...2NaOH+Cl2→NaCl+NaOCl+H2O

Fluorine is an element that belongs to the halogen group in the periodic table. It has an atomic number of 9, and its electron configuration is 1s^2 2s^2 2p^5. Fluorine is highly electronegative, meaning it has a strong tendency to attract electrons towards itself when it forms chemical bonds. This property is due to its relatively small atomic size and high effective nuclear charge.

Fluorine has a total of 7 valence electrons, which are electrons in its outermost energy level (2s^2 2p^5). In order to achieve a stable electron configuration, fluorine tends to gain one electron to complete its octet. By gaining one electron, fluorine achieves a stable electron configuration similar to the nearest noble gas, neon (1s^2 2s^2 2p^6).

Fluorine's strong electronegativity and its tendency to gain electrons result in it having only one common oxidation state, which is -1. In this oxidation state, fluorine gains one electron to achieve a stable configuration of 1s^2 2s^2 2p^6. This oxidation state is commonly observed in compounds where fluorine acts as an anion, such as in the compound sodium fluoride (NaF). In NaF, fluorine gains an electron from sodium to form the F- ion.

It is important to note that although fluorine is highly electronegative and tends to gain electrons, it does not have the capability to lose electrons easily and form positive oxidation states. This is because fluorine's valence shell is almost full, and losing electrons would require a significant amount of energy.

In conclusion, fluorine has only one common oxidation state, which is -1. This is due to its strong electronegativity and its tendency to gain one electron to achieve a stable electron configuration.

Gas Bleaching of Flowers by Reduction and Oxidation

Reduction and oxidation reactions play a crucial role in various chemical processes. In the context of bleaching the color of flowers, two gases are involved, one causing bleaching by reduction and the other by oxidation. Let us examine the given options to identify the correct gases.

Option A: SO2 and Cl2
Option B: CO2 and Cl2
Option C: NO and Cl2
Option D: H2S and Br2

Based on the given options, the correct gases are SO2 and Cl2.

Explanation:

1. Reduction and Oxidation Reactions:
Reduction is a process that involves the gain of electrons or a decrease in oxidation state, while oxidation is a process that involves the loss of electrons or an increase in oxidation state. In the context of bleaching, reduction and oxidation reactions are responsible for altering the color of flowers.

2. SO2 and Cl2:
Sulfur dioxide (SO2) is an example of a reducing agent. It can bleach the color of flowers by undergoing reduction reactions. SO2 is capable of reacting with pigments responsible for the color of flowers and reducing them, resulting in a loss of color.

Chlorine gas (Cl2), on the other hand, is an example of an oxidizing agent. It can bleach the color of flowers by undergoing oxidation reactions. Cl2 can react with pigments responsible for the color of flowers and oxidize them, leading to a loss of color.

Therefore, the correct answer is option A: SO2 and Cl2. SO2 acts as a reducing agent, while Cl2 acts as an oxidizing agent to bleach the color of flowers.

In summary, reduction and oxidation reactions are involved in bleaching the color of flowers. Sulfur dioxide (SO2) acts as a reducing agent, while chlorine gas (Cl2) acts as an oxidizing agent to bleach the color of flowers.

Explanation:

Capping of hnRNA:
- The process of adding a modified nucleotide (menthyl guanosine triphosphate) to the 5' end of hnRNA is known as capping.
- This modification protects the mRNA from degradation and helps in the recognition of the mRNA by ribosomes during translation.

Function of capping:
- The capping of hnRNA is essential for the proper processing and translation of mRNA.
- It also plays a role in regulating gene expression and facilitating the export of mRNA from the nucleus to the cytoplasm.

Importance of capping:
- Capping helps in the stability of mRNA by protecting it from exonuclease degradation.
- It also assists in the initiation of translation by providing a recognition signal for ribosomes.
Therefore, in the given question, the addition of menthyl guanosine triphosphate to the 5' end of hnRNA is a part of the capping process, which is crucial for the proper functioning of mRNA in gene expression.

The question is incomplete as it does not provide the options for the van der Waals forces. Please provide the options so I can assist you further.

D. Thermal stability (HF HCI HBr HI)

Explanation:
Thermal stability refers to the ability of a compound to withstand high temperatures without undergoing decomposition. In general, thermal stability decreases down a group and increases across a period.

HF (Hydrogen fluoride)
- HF is thermally stable and does not decompose easily at high temperatures.
- This is due to the strong hydrogen bonding present in HF, which results in a high boiling point and thermal stability.

HCI (Hydrogen chloride)
- HCI is also thermally stable and does not decompose easily at high temperatures.
- Similar to HF, HCI exhibits strong hydrogen bonding, resulting in a high boiling point and thermal stability.

HBr (Hydrogen bromide)
- HBr is less thermally stable compared to HF and HCI.
- It can decompose at high temperatures to form hydrogen and bromine gases.
- This is because the strength of hydrogen bonding in HBr is weaker than that in HF and HCI, resulting in a lower boiling point and lower thermal stability.

HI (Hydrogen iodide)
- HI is the least thermally stable among the given options.
- It decomposes readily at high temperatures to form hydrogen and iodine gases.
- The strength of hydrogen bonding in HI is the weakest among the options, leading to a lower boiling point and lower thermal stability.

Conclusion:
Based on the above explanations, the incorrect option among the given properties is option D, which states that HI is thermally stable. In reality, HI is the least thermally stable compound among HF, HCI, HBr, and HI.

Polycistronic mRNA in Bacteria and Prokaryotes
Polycistronic mRNA refers to a type of messenger RNA that carries the information for multiple genes in a single transcript. This phenomenon is commonly observed in bacteria and prokaryotes.

Bacteria
- In bacteria, the genetic material is organized in a single circular chromosome, and the transcription and translation processes are coupled.
- Bacterial mRNA is often polycistronic, meaning that a single mRNA molecule can encode multiple proteins that are part of the same functional pathway or protein complex.
- This arrangement allows for the coordinated expression of multiple genes that are involved in related cellular functions.

Prokaryotes
- Prokaryotes, including bacteria, lack a true nucleus and have a simpler organization of genetic material compared to eukaryotic cells.
- In prokaryotes, such as archaea, polycistronic mRNA is also common, serving as an efficient way to regulate gene expression and coordinate the synthesis of multiple proteins.
- The presence of polycistronic mRNA in prokaryotes allows for the rapid adaptation to changing environmental conditions and the simultaneous expression of genes that are functionally related.

Conclusion
Polycistronic mRNA is a characteristic feature of bacteria and prokaryotes, where it plays a crucial role in the regulation of gene expression and coordination of protein synthesis. This unique feature highlights the differences in gene expression mechanisms between prokaryotic and eukaryotic cells.

Answer:

Promoter:
The site on a DNA molecule where RNA polymerase binds during transcription is called a promoter. Promoters are specific sequences of DNA that are located near the beginning of a gene.

Function of Promoter:
- Promoters play a crucial role in initiating the process of transcription by providing a binding site for RNA polymerase.
- They help in determining the starting point for transcription and also regulate the expression of genes by controlling the rate of transcription.

Types of Promoters:
- There are different types of promoters such as constitutive promoters, which are always active, and inducible promoters, which are activated in response to specific signals or environmental conditions.

Structure of Promoter:
- Promoters consist of several components, including the TATA box, which is a short sequence of DNA that helps in positioning RNA polymerase at the correct site to start transcription.
- Other elements like enhancers and silencers may also be present in the promoter region, which can influence transcriptional activity.

Importance of Promoter:
- Promoters are essential for the proper regulation of gene expression in cells. They ensure that genes are transcribed at the right time and in the right amount, which is crucial for the normal functioning of living organisms.
In conclusion, the promoter is a critical component of the transcription process as it serves as the binding site for RNA polymerase and helps in initiating the synthesis of RNA from DNA.

The correct answer is option 'C': Transcription starts with the promoter region and ends in the terminator region. Let's break down the process of transcription and explain why this is the correct answer.

Transcription is the first step in gene expression, where the information encoded in DNA is transcribed into RNA. This process involves several key regions and factors that play important roles. Let's discuss each option and why they are correct or incorrect.

a) Starts with TATA box:
- The TATA box is a DNA sequence found upstream of the transcription start site in many eukaryotic genes. It serves as a binding site for transcription factors and helps in the initiation of transcription.
- While the TATA box is an important element in the promoter region, it is not the starting point of transcription. Therefore, option 'a' is incorrect.

b) Starts with palindromic regions and ends with rho factor:
- Palindromic regions are DNA sequences that read the same on both strands when oriented in the same direction. They can be involved in various regulatory processes, but they are not the starting points of transcription.
- The rho factor is a protein involved in the termination of transcription in prokaryotes. It binds to the RNA molecule and causes the release of the RNA from the DNA template.
- While these regions and factors are involved in transcription, they do not mark the starting point. Therefore, option 'b' is incorrect.

c) Starts with promoter region and ends in terminator region:
- The promoter region is the DNA sequence where RNA polymerase binds and initiates transcription. It contains specific sequences and elements, such as the TATA box, that help in the recognition and binding of transcription factors.
- The terminator region is a DNA sequence that signals the end of transcription. It contains signals for the termination of RNA synthesis and the release of the RNA molecule.
- Therefore, option 'c' is correct as transcription starts with the promoter region and ends in the terminator region.

d) Starts with CAAT region:
- The CAAT box is another DNA sequence found in the promoter region of many eukaryotic genes. It is involved in the binding of transcription factors and the regulation of gene expression.
- While the CAAT region is important in the promoter, it is not the starting point of transcription. Therefore, option 'd' is incorrect.

In summary, transcription starts with the promoter region and ends in the terminator region. These regions contain specific sequences and elements that play crucial roles in the initiation and termination of transcription.