Problem 114 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements is correct? (a) the metal ion present in vitamin \(\mathrm{B}_{12}\) is \(\mathrm{Zn}^{2+}\) (b) in photosynthesis \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) are converted into carbohydrates in presence of sunlight (c) in haemoglobin the oxidation state of \(\mathrm{Fe}\) is \(+6\). (d) methyl salicylate is known as aspirin

Step-by-Step Solution

Answer

Statement (b) about photosynthesis is correct.

Step 1: Analyze Statement (a)

Statement (a) claims that the metal ion present in vitamin \( \mathrm{B}_{12} \) is \( \mathrm{Zn}^{2+} \). Vitamin \( \mathrm{B}_{12} \), also known as cobalamin, contains a cobalt ion \( \mathrm{Co} \). Therefore, statement (a) is incorrect as it incorrectly lists zinc (\( \mathrm{Zn}^{2+} \)) instead of cobalt.

Step 2: Analyze Statement (b)

Statement (b) suggests that in photosynthesis, \( \mathrm{CO}_{2} \) and \( \mathrm{H}_{2} \mathrm{O} \) are converted into carbohydrates in the presence of sunlight. This is indeed correct as photosynthesis uses these reactants along with sunlight to produce glucose and oxygen. Thus, statement (b) is correct.

Step 3: Analyze Statement (c)

Statement (c) asserts that the oxidation state of iron (\( \mathrm{Fe} \)) in haemoglobin is \(+6\). In haemoglobin, iron typically exists in the +2 (ferrous) or +3 (ferric) oxidation states, not +6. Therefore, statement (c) is incorrect.

Step 4: Analyze Statement (d)

Statement (d) claims that methyl salicylate is known as aspirin. However, methyl salicylate is not the same as aspirin. Aspirin is acetylsalicylic acid, while methyl salicylate is often called oil of wintergreen. Therefore, statement (d) is incorrect.

Key Concepts

Vitamin B12 Cobalt Ion

Vitamin B12, also known as cobalamin, is an essential nutrient that plays a significant role in maintaining nerve function and the production of DNA. One of the unique features of vitamin B12 is its molecular structure which includes a cobalt ion. The presence of the cobalt ion is so central that it gives vitamin B12 its chemical name, 'cobalamin.'

Unlike zinc ions, which are mentioned incorrectly in the original exercise statement, the cobalt ion in vitamin B12 is crucial for the compound's functions:

• It helps in the conversion of homocysteine to methionine, which is important for DNA synthesis.
• It is involved in the formation of red blood cells and the maintenance of the nervous system.
• It is essential for brain health and the synthesis of neurotransmitters.

Cobalamin’s activity in the body emphasizes the importance of the cobalt ion in its structure, distinguishing it from other vitamins and underscoring its biological significance.

Photosynthesis Process

Photosynthesis is a remarkable process carried out by plants, algae, and some bacteria. It allows these organisms to convert light energy, typically from the sun, into chemical energy stored in carbohydrates like glucose. The process takes place primarily in the chloroplasts of plant cells.

During photosynthesis, plants take in carbon dioxide (CO_2) from the air and water (H2O) from the soil. The energy from sunlight splits the water molecules and helps convert the carbon dioxide into glucose, a simple sugar that plants use as food. Oxygen, a byproduct of this process, is released into the atmosphere.

Some key points about photosynthesis include:

• It occurs in two stages: the light-dependent reactions and the Calvin cycle or light-independent reactions.
• In the light-dependent reactions, sunlight is captured to produce energy-rich molecules ATP and NADPH.
• In the Calvin cycle, ATP and NADPH are used to convert CO2 into glucose.

Photosynthesis is not just fundamental for the survival of plants, but it is also vital for life on Earth as it provides the oxygen we breathe and forms the base of food chains.

Haemoglobin Iron Oxidation States

Haemoglobin is a protein found in red blood cells, responsible for the transport of oxygen throughout the body. A crucial component of haemoglobin is the iron (Fe) ion, which can exist in different oxidation states.

In haemoglobin, iron usually exists in either the +2 (ferrous) or +3 (ferric) oxidation states, which are far more stable and functional in biological systems than the +6 oxidation state incorrectly mentioned in the original exercise.

Some essential details about the iron's role in haemoglobin include:

• When iron is in the +2 state in haemoglobin, it can bind to oxygen molecules. This allows haemoglobin to pick up oxygen in the lungs and transport it to tissues.
• In the +3 state, iron forms methemoglobin, which doesn't effectively bind oxygen but is transformed back to haemoglobin in the body.
• The dynamic transition between these states facilitates oxygen transport and delivery within the body, crucial for cellular respiration and energy production.

Understanding the correct oxidation states of iron in haemoglobin is paramount for comprehending how oxygen is transported in the bloodstream efficiently.