Hydrogen — Advanced Notes & 50 MCQs

1. The most abundant isotope of hydrogen is:

1. Deuterium
2. Tritium
3. Protium (¹H) ✅
4. Hydronium

2. Which method produces hydrogen industrially on the largest scale?

1. Electrolysis of water
2. Steam methane reforming (SMR) ✅
3. Thermal decomposition of water
4. Photolysis

3. The bond in H2 is best described as:

1. Ionic
2. Metallic
3. Covalent (nonpolar) ✅
4. Hydrogen bond

4. Heavy water used in nuclear reactors contains which isotope of hydrogen?

1. Protium
2. Deuterium (²H) ✅
3. Tritium
4. Hydride ion

5. Which of the following is not a hydride type?

1. Ionic hydride
2. Interstitial hydride
3. Covalent hydride is a type (so trick question) ✅
4. Metallic hydride

6. Hydrogen reacts with oxygen to form water. The reaction is:

1. Endothermic
2. Highly exothermic ✅
3. Neutral
4. Reversible without energy

7. Which gas is used as a fuel in fuel cells to generate electricity with water as product?

1. Methane
2. Hydrogen ✅
3. Carbon monoxide
4. Oxygen

8. Hydrogen chloride gas reacts with hydrogen to form HCl? Which statement is correct?

1. H2 + HCl → 2HCl
2. No direct formation; HCl is formed from H2 and Cl2 usually ✅
3. H2 + HCl → H3Cl
4. H2 reduces HCl to Cl-

9. An important laboratory method for preparing hydrogen is:

1. Reaction of acid with carbonate
2. Reaction of dilute acid with zinc (Zn + 2HCl → ZnCl2 + H2) ✅
3. Electrolysis of molten salts only
4. Thermal cracking of water vapor

10. Hydrogen bonding is strongest in which of these?

1. H2
2. Water (H2O) ✅
3. HCl
4. CH4

11. Hydride ion (H-) behaves as:

1. Acid
2. Base / strong reducing agent ✅
3. Oxidizing agent
4. Neutral spectator

12. Tritium is radioactive. Its common application is:

1. Fuel in cars
2. Tracer and in nuclear studies ✅
3. Food preservative
4. As a non-radioactive isotope

13. Which statement about hydrogen in atmosphere is correct?

1. Major component of atmosphere
2. Very low concentration, escapes to space due to lightness ✅
3. Atmospheric hydrogen is radioactive
4. Cannot form compounds in atmosphere

14. Which hydride is ionic in nature?

1. CH4
2. NaH ✅
3. BF3·H2 (complex)
4. AlH3

15. Hydrogen acts as a reducing agent when it:

1. Gains oxygen
2. Donates electrons / removes oxygen from metal oxides ✅
3. Reacts with water to form H3O+
4. Forms hydronium ion only

16. The standard enthalpy of formation of H2 (gas) is:

1. Highly negative
2. Zero (element in standard state) ✅
3. Positive
4. Undefined

17. Which metal hydride is used for hydrogen storage due to reversible uptake?

1. NaH
2. MgH2 and certain intermetallic hydrides ✅
3. HCl
4. H2O

18. In the Haber process, hydrogen combines with nitrogen to form:

1. Hydrazine
2. Ammonia (NH3) ✅
3. Urea directly
4. Nitric acid

19. Which catalyst is commonly used for hydrogenation of vegetable oils?

1. Cu
2. Ni (Nickel) ✅
3. Hg
4. Ag

20. Hydrogen can reduce metal oxides because it:

1. Is a strong oxidizing agent
2. Acts as reducing agent by combining with oxygen to form water ✅
3. Increases oxidation state of metal
4. Removes electrons from metals

21. The flame of hydrogen in air is:

1. Bright yellow
2. Pale blue / nearly invisible in daylight ✅
3. Green
4. Red

22. Which reaction demonstrates amphoteric behavior of hydrogen?

1. H2 + O2 → H2O
2. Hydrogen forms both H+ (as in acids) and H- (in hydrides) ✅
3. H2 forming only hydrides
4. Hydrogen cannot be amphoteric

23. Which product is formed when hydrogen reacts with chlorine in presence of light?

1. H2Cl2
2. Hydrogen chloride (HCl) ✅
3. Hydrogen peroxide
4. Chlorine hydride polymer

24. Which gas must be removed/purified when producing hydrogen by electrolysis of water to get high purity H2?

1. Oxygen only
2. Oxygen (and moisture) — remove to avoid recombination ✅
3. Nitrogen only
4. Argon

25. In proton-exchange membrane fuel cells, hydrogen is supplied to:

1. Cathode
2. Anode (H2 → 2H+ + 2e-) ✅
3. Salt bridge
4. Both electrodes equally

26. Which of the following is true about hydrides of transition metals (interstitial hydrides)?

1. They are ionic
2. They often show metallic conductivity and non-stoichiometry ✅
3. They always decompose explosively in air
4. They are covalent molecular species

27. Which hydride is covalent and gaseous at room temperature?

1. NaH
2. CH4 (methane) as a covalent hydride example ✅
3. CaH2
4. MgH2

28. Which technique separates hydrogen from mixture gases by adsorbing impurities at high pressure and desorbing them at low pressure?

1. Cryogenic distillation
2. Pressure swing adsorption (PSA) ✅
3. Membrane electrolysis
4. Fractional crystallization

29. Which is true about hydrogen embrittlement?

1. Hydrogen makes metals more ductile
2. Hydrogen can diffuse into metals and cause cracking/brittle failure ✅
3. Only occurs in plastics
4. Prevents corrosion always

30. Which equation gives the mass of hydrogen produced in electrolysis as function of charge passed?

1. Ideal gas law
2. Faraday's law (m = (Q × M) / (n × F)) ✅
3. Arrhenius equation
4. Nernst equation

31. Hydrogen peroxide (H2O2) can be formed from hydrogen and oxygen under catalysis. H2O2 acts as:

1. Only oxidizing agent
2. Both oxidizing and reducing agent ✅
3. Only reducing agent
4. Inert gas

32. Which statement about hydrogen's electronegativity is correct?

1. Hydrogen is highly electronegative like fluorine
2. Hydrogen has intermediate electronegativity (~2.1) ✅
3. Hydrogen is electropositive always
4. Hydrogen has zero electronegativity

33. Which compound is a proton donor (Brønsted acid) involving hydrogen?

1. NH3
2. HCl ✅
3. CH4
4. H2 (gas)

34. The reaction of hydrogen with nitrogen in Haber process is catalyzed by:

1. Pt only
2. Fe-based catalysts (with promoters) ✅
3. Hg catalyst
4. No catalyst used

35. Which statement is true for hydrogen's standard electrode potential (2H+ + 2e- → H2)?

1. It is +0.76 V
2. It is defined as 0.00 V (SHE) ✅
3. It varies with concentration only
4. It is negative for all solutions

36. Which is not a use of hydrogen?

1. Fuel in fuel cells
2. Production of ammonia
3. As a primary refrigerant in household refrigerators ✅
4. Hydrogenation in industry

37. Which of the following hydrides is unstable and decomposes to give hydrogen on heating?

1. LiH (stable ionic)
2. NH3BH3 (ammonia borane releases H2 on heating) ✅
3. NaH (stable ionic)
4. CH4 (stable gas)

38. Which factor increases ease of hydrogen diffusion through metals?

1. Larger atomic size of metal
2. High temperature and small lattice gaps ✅
3. Low temperature
4. Presence of oxide layer always

39. Which is a laboratory source of hydrogen other than acid-metal reactions?

1. Decomposition of NH4Cl
2. Reaction of NaBH4 with water/alcohols ✅
3. Reaction of CO2 with water
4. Calcination of limestone

40. Which gas forms a water molecule with hydrogen upon combustion?

1. Nitrogen
2. Oxygen ✅
3. Carbon dioxide
4. Helium

41. Which statement about hydrogen's solubility in water is correct?

1. Hydrogen is highly soluble in water
2. Hydrogen is sparingly soluble in water ✅
3. Hydrogen reacts with water to form acid
4. Hydrogen is insoluble and forms hydrate

42. Which industrial process consumes hydrogen as a reactant on large scale?

1. Sulfuric acid production
2. Ammonia synthesis (Haber-Bosch) ✅
3. Chlor-alkali process
4. Electroplating only

43. Which compound is produced by hydrogenation of vegetable oils?

1. Alcohols
2. Saturated fats (hydrogenated oils) ✅
3. Ammonia
4. Hydrochloric acid

44. Which process increases hydrogen production without CO2 emission when using renewable electricity?

1. Steam methane reforming
2. Water electrolysis using renewable electricity (green hydrogen) ✅
3. Coal gasification
4. Partial oxidation of oil

45. Which is a potential environmental concern with hydrogen economy?

1. Hydrogen causes greenhouse warming directly
2. Indirect effects: leakage can affect atmospheric chemistry and longevity; production routes may emit CO2 if fossil fuels used ✅
3. No concerns at all
4. Hydrogen depletes ozone layer directly

46. Which species is proton in aqueous solution?

1. H2
2. H+ (often exists as hydronium H3O+) ✅
3. H-
4. Neutral hydrogen atom

47. Which statement about hydrogen's thermal conductivity is correct?

1. Hydrogen has very low thermal conductivity
2. Hydrogen has very high thermal conductivity compared to many gases ✅
3. Hydrogen is thermal insulator
4. Thermal conductivity equals that of air

48. Which of the following is a storage challenge for hydrogen fuel?

1. Low energy per mass
2. Very low volumetric energy density at ambient conditions — requires compression/liquefaction or solid storage ✅
3. Inability to react with oxygen
4. Hydrogen is non-flammable

49. Which reagent can act as a hydrogen donor in organic reductions (transfer hydrogenation)?

1. O2
2. Formic acid or isopropanol (as hydrogen donors) ✅
3. HCl
4. NaCl