Which of the following statements are NOT correct?
A. Hydrogen is used to reduce heavy metal oxides

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Question

Which of the following statements are NOT correct?
A. Hydrogen is used to reduce heavy metal oxides to metals.
B. Heavy water is used to study reaction mechanism.
C. Hydrogen is used to make saturated fats from oils.
D. The H–H bond dissociation enthalpy is lowest as compared to a single bond between two atoms of any elements.
E. Hydrogen reduces oxides of metals that are more active than iron.
Choose the most appropriate answer from the options given below:
(1) B, C, D, E only
(2) B, D only
(3) D, E only
(4) A, B, C only

Accepted Answer

Correct Answer: C — D, E only (are NOT correct)Step-by-step Solution:A (CORRECT statement): Hydrogen is indeed used to reduce heavy metal oxides (like CuO, WO₃, NiO) to their metals: CuO + H₂ → Cu + H₂O. This is a common industrial/laboratory process.B (CORRECT statement): Heavy water (D₂O) is used to study reaction mechanisms by isotopic labeling (deuterium tracing). D₂O is also used in NMR spectroscopy as a solvent and in nuclear reactors as a moderator.C (CORRECT statement): Hydrogen is used in the hydrogenation of vegetable oils (unsaturated fats) to convert them into saturated fats (vanaspati/margarine) using a nickel catalyst: C=C + H₂ → C–C. This is catalytic hydrogenation.D (NOT CORRECT — this is the wrong statement): The H–H bond dissociation enthalpy is 436 kJ/mol. Far from being the lowest, this is one of the highest single bond energies! For reference, F–F is only ~158 kJ/mol (actually one of the lowest). So the claim that H–H bond energy is the lowest is false.E (NOT CORRECT — this is the wrong statement): Hydrogen can reduce only the oxides of metals that are less active (less electropositive) than hydrogen — i.e., metals below hydrogen in the activity series (such as Cu, Ag, Pb). It CANNOT reduce oxides of metals more active than iron (like Al, Mg, Na, K) because those metals have very stable oxides that H₂ cannot reduce under normal conditions.Key Concepts:H–H bond dissociation enthalpy = 436 kJ/mol (one of the highest for single bonds; for comparison, F–F = 158 kJ/mol, Cl–Cl = 243 kJ/mol).Activity series: K > Na > Ca > Mg > Al > Zn > Fe > Ni > Sn > Pb > H > Cu > Ag > Au. H₂ reduces only oxides of metals placed below Fe (i.e., metals less active than Fe).Heavy water (D₂O): Used in nuclear reactors (moderator/coolant), isotopic labeling studies, NMR spectroscopy.Hydrogenation of oils: Ni catalyst, converts liquid oils → solid fats (margarine).

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