General Chemistry

Step 1: Understanding the Effect of Substituents on Acidity.
The acidic strength of carboxylic acids is influenced by the electron-withdrawing or electron-donating nature of substituents attached to the benzene ring (in case of substituted carboxylic acids). Electron-withdrawing groups (like halogens) increase the acidity of carboxylic acids by stabilizing the negative charge on the conjugate base (the carboxylate anion).
Electron-withdrawing groups (like ) make the acid stronger.
Electron-donating groups (like ) reduce the acidity.
Step 2: Analyze the compounds.
A. : The methyl group is an electron-donating group, which decreases the electron density on the carboxyl group, reducing its acidity. Hence, this is the weakest acid.
B. : The group is electron-withdrawing but is attached to the second carbon. It increases the acidity slightly compared to A.
C. : Two chlorine atoms attached to the carboxyl group significantly withdraw electron density, making the acid stronger than A and B.
D. : With three chlorine atoms, this compound is even more acidic than C due to a greater electron-withdrawing effect.
E. : Fluorine is a very strong electron-withdrawing group, and having three fluorine atoms attached to the carboxyl group makes this compound the most acidic among the options.
Step 3: Conclusion.
The order of acidic strength is:

Thus, the correct answer is (2) E > D > C > B > A.

Step 1: Understanding Aromatic Compounds.
Aromatic compounds follow the Huckel rule, which states that for a compound to be aromatic, it must:
Be cyclic,
Be planar,
Contain a conjugated system of alternating single and double bonds (alternating bonds are a characteristic of a conjugated system),
Contain a total number of π-electrons that follow the formula , where is a non-negative integer (this is called the Huckel criterion for aromaticity).
Step 2: Analyze each option.
Option (1) A: This compound is a six-membered carbon ring with conjugated double bonds and follows the Huckel rule with 6 π-electrons, which satisfy the rule (for ). Therefore, A is aromatic.
Option (2) B: This compound has a positive charge on one carbon and a negative charge on another, indicating that it is not a simple aromatic ring with conjugated bonds. Hence, it is not aromatic.
Option (3) C: This compound has no conjugation and does not satisfy the Huckel rule, so it is not aromatic.
Option (4) D: This is a simple six-membered ring with no alternating single and double bonds. This structure does not satisfy the Huckel criterion for aromaticity.
Step 3: Conclusion.
The correct aromatic compound is Option A.

Step 1: Understand what Vitamin B₁₂ is.
Vitamin B₁₂, also known as cobalamin, is a complex organometallic compound that plays an essential role in red blood cell formation, neurological function, and DNA synthesis.
Step 2: Identify the central metal ion in Vitamin B₁₂.
The name “cobalamin” comes from cobalt (Co), which is the central metal ion in the corrin ring of the Vitamin B₁₂ molecule. The cobalt atom is coordinated at the center of this ring, which is similar in structure to a porphyrin ring but slightly contracted.
Step 3: Eliminate the other options.
Mn (Manganese): Not present in Vitamin B₁₂.
Zn (Zinc): Important in enzymes like carbonic anhydrase, but not in B₁₂.
Cu (Copper): Found in proteins like ceruloplasmin but not in B₁₂.
Step 4: Confirm the correct answer.
Only Cobalt (Co) is associated with Vitamin B₁₂, making option (2) the correct one.

Step 1: Understand the composition of natural rubber.
Natural rubber is a polymer of isoprene, which is chemically known as 2-methyl-1,3-butadiene. The polymerization of isoprene produces polyisoprene, which is the principal component of natural rubber.
Step 2: Understand what synthetic rubber neoprene is.
Neoprene is a type of synthetic rubber formed by the polymerization of chloroprene, which is chemically called 2-chloro-1,3-butadiene. This polymer is used for making hoses, gaskets, and wetsuits due to its high resistance to oil, heat, and weathering.
Step 3: Match the correct monomers.
Natural rubber → monomer = 2-methyl-1,3-butadiene (isoprene)
Neoprene → monomer = 2-chloro-1,3-butadiene (chloroprene)
Step 4: Analyze the options.
Option (1): Incorrect — Natural rubber is not made from 1,3-butadiene.
Option (2): Incorrect — This reverses the monomers of natural and synthetic rubber.
Option (3): Correct — Matches both monomers accurately.
Option (4): Incorrect — Acrylonitrile is used in other polymers like nitrile rubber, not natural rubber.

Step 1: Understand Ocean Acidification
Ocean acidification refers to the process by which the ocean becomes more acidic due to an increase in the concentration of carbon dioxide (CO₂) in the atmosphere. This CO₂ dissolves in seawater and reacts with water molecules to form carbonic acid, which then dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO₃^-).

Step 2: The chemical reaction responsible for ocean acidification
The chemical equation that describes the formation of carbonic acid in seawater is:
CO2 + H2O → H2CO3 → H+ + HCO3-
This increase in hydrogen ion concentration (H⁺) leads to a decrease in pH, causing ocean water to become more acidic.

Step 3: Analyze the options

Option (1): Carbonic acid
This is the correct answer because carbonic acid is formed when CO₂ dissolves in water, and it plays a major role in ocean acidification. It is the primary acid involved in this process.

Option (2): Sulphuric acid
Sulphuric acid is not involved in ocean acidification. It is typically formed from sulfur dioxide (SO₂) emissions but does not play a significant role in the acidification of oceans.

Option (3): Phosphoric acid
Phosphoric acid is not involved in ocean acidification. It is used in fertilizers and industrial processes but does not affect the ocean's pH in the same way as carbonic acid.

Option (4): Nitric acid
Nitric acid is also not involved in ocean acidification. While it can contribute to acid rain, its role in ocean acidification is minimal compared to carbonic acid.

Step 1: Analyze reactivity with oxygen.
Aluminium (Al) is highly reactive with oxygen and forms a protective layer of aluminium oxide (Al O ).
Copper (Cu) also reacts with oxygen, though less vigorously, forming copper oxides (CuO and Cu O) over time.
Step 2: Rule out incorrect options.
Option (1): Au (Gold) and Pt (Platinum) are noble metals, known for their low reactivity and resistance to oxidation.
Option (2): Ne (Neon) and Ar (Argon) are noble gases and completely inert under normal conditions—they do not form oxides.
Option (4): Pt, as discussed, is not reactive enough to form oxides readily. Hence, the correct answer is (3) Al and Cu.