Minerals and Nutrients

Talc is a hydrated magnesium silicate mineral with the chemical formula Mg3Si4O10(OH)2, composed of magnesium, silicon, and oxygen. It is used in talcum powder and cosmetics due to its softness and ability to absorb moisture. Options A, B, and D incorrectly list elements like zinc, calcium, and tin which are not found in talc.

Active mineral absorption requires energy (ATP) because minerals are moved against their concentration gradient from soil to root cells. This is an active transport process facilitated by carrier proteins in the cell membrane. Active water absorption is passive (osmosis), photophosphorylation produces ATP but doesn't directly drive mineral uptake, and vascular bundle cells facilitate transport but don't power it.

Nitrogen deficient plants will also exhibit a purple appearance on the stems, petioles and underside of leaves from an accumulation of anthocyanin pigments.

 It is a primary macronutrient of the plants.

Potassium regulates the opening and closing of the stomata by a potassium ion pump. Since stomata are important in water regulation, potassium reduces water loss from the leaves and increases drought tolerance.

Vitamin B12, also known as cobalamin, is the only vitamin that contains cobalt as an essential component of its molecular structure. The cobalt atom sits at the center of the corrin ring and is crucial for B12's biological activity. Iron is important for hemoglobin, magnesium is a cofactor for many enzymes, and zinc is involved in immune function, but only cobalt is integral to vitamin B12.

PCR (Polymerase Chain Reaction) requires Mg++ ions as an essential cofactor for Taq polymerase and other DNA polymerases used in PCR. Mg2+ is required for enzyme activity and stabilizes the DNA duplex. The reaction buffer contains MgCl2. Lithium, calcium, and sodium ions are not required for PCR - in fact, calcium can be inhibitory and the others are not part of the standard reaction mix.

PCR requires magnesium ions (Mg2+) as essential cofactors for Taq polymerase activity. Mg2+ stabilizes the DNA duplex and is required for the polymerase to function properly. The concentration of Mg2+ also affects primer annealing and specificity. Lithium, calcium, and sodium are not required cofactors for PCR.

Pyridoxal oxidase employs molybdenum as cofactor.

Vertebrate bones are primarily composed of calcium phosphate in the form of hydroxyapatite crystals, which provides hardness and rigidity. Calcium carbonate is the main component of invertebrate shells like those of mollusks. Sodium chloride and potassium hydroxide are not structural components of bone tissue.

Micro-nutrients are required in minute quantities but are as important as macro-nutrients. 

Nickel (Ni) is an essential cofactor for urease, the enzyme that catalyzes urea hydrolysis in nitrogen metabolism. Molybdenum activates nitrate reductase and nitrogenase, while zinc and boron support other enzymatic functions.

Mobile mineral elements in plants can be translocated from older to younger tissues when deficient. Molybdenum (Mo) is mobile, while Calcium (Ca), Iron (Fe), and Copper (Cu) are relatively immobile - once deposited in tissues, they cannot be easily moved to new growth.

This is the correct answer. Zinc is not commonly present in protoplasm.

This is the correct answer. Plants do not require hydrogen for their existence.