Problem 143 - A Complete Resource Book in Chemistry for JEE Main

Question

Among the following, the correct statement is (a) Phosphates have no biological significance in humans (b) Between nitrates and phosphates, phosphates are less abundant in earth's crust (c) Between nitrates and phosphates, nitrates are less abundant in earth's crust (d) Oxidation of nitrates is possible in soil.

Step-by-Step Solution

Answer

The correct statement is (c). Nitrates are less abundant than phosphates in Earth's crust.

Step 1: Analyze Each Statement

We need to evaluate each statement to determine its accuracy. Let's first examine statement (a): 'Phosphates have no biological significance in humans.' This is incorrect because phosphates are vital for many biological processes in humans, including ATP production and bone formation.

Step 2: Compare Abundance in Earth's Crust

Statement (b) says: 'Between nitrates and phosphates, phosphates are less abundant in earth's crust.' This is incorrect because phosphates are generally more abundant in the earth's crust than nitrates.

Step 3: Evaluate Nitrate and Phosphate Abundance

Statement (c) claims: 'Between nitrates and phosphates, nitrates are less abundant in earth's crust.' This is correct because phosphates are more prevalent in the crust due to minerals like apatite, whereas nitrates are commonly found dissolved and not as a prevalent mineral form.

Step 4: Assess Nitrate Oxidation

Finally, statement (d): 'Oxidation of nitrates is possible in soil,' is incorrect. Nitrates themselves are already in an oxidized form (NO3-) and undergo reduction rather than oxidation in soil processes.

Key Concepts

Biological Significance of Phosphates

Phosphates play a crucial role in various biological functions, especially within the human body. They form an integral part of adenosine triphosphate, commonly known as ATP, which is essentially the energy currency of cells. Without phosphates, the smooth functioning of metabolic processes would be compromised.

Moreover, phosphates are fundamental to bone health, contributing to the formation of bone mineral and the overall regulation of bone density. This occurs in conjunction with calcium to form calcium phosphate salts, lending strength and structure to bones and teeth.

Phosphates are also critical in DNA and RNA, forming structural units that help store and transfer genetic information. They act as buffering agents to maintain pH levels in blood and other bodily fluids, crucial for normal cellular functions. Their biological importance cannot be overstated, as they're involved in numerous cellular and physiological activities.

Earth's Crust Composition

The Earth's crust is composed largely of different types of oxides and silicates, among which phosphates are more prevalent compared to nitrates. Phosphate minerals, particularly apatites, are commonly found and contribute significantly to the crust's composition.

These minerals not only make phosphates more abundant but also play a role in geological and biological ecosystems. Nitrates, on the other hand, are generally found dissolved in water bodies rather than as solid minerals, making them less abundant in the Earth's crust.

Phosphates' solid-state presence in the crust leads to their easier extraction and application in agriculture and industry, which greatly supports their abundance and significance. Their presence in the lithosphere, hydrosphere, and biosphere highlights their contribution to life's chemical basis and Earth's geological processes.

Nitrate Oxidation

Nitrates are an oxidized form of nitrogen, represented by the chemical formula NO3-. In soils, instead of undergoing oxidation, nitrates participate in reduction processes mainly through denitrification.

Denitrification involves the conversion of nitrates to nitrogen gas, which is facilitated by bacteria in anaerobic conditions. This process is critical in the nitrogen cycle, helping to release nitrogen back into the atmosphere from the soil.

While oxidation is intrinsic to several nutrient cycles, nitrate oxidation does not naturally occur due to its already oxidized state. Understanding these dynamics helps us appreciate nutrient cycling in ecosystems and the specific roles different forms of nitrogen play in soil chemistry.