NEET Chemistry: Hydrogen questions with solutions

Q1. Which of the following can be used to prepare hydrogen gas in the laboratory?

1. Mercuric oxide
2. Acid plus zinç
3. Potassium chlorate
4. Carbon disulfide E. Benzene

Answer: Acid plus zinç

Zinc reacts with dilute acids to produce hydrogen gas, making it a common laboratory preparation method. The other options are used for different reactions or do not generate hydrogen under normal lab conditions.

Q2. Heavy water is obtained by?

1. boiling water
2. heatiing \( H_{2} O_{2} \)
3. Prolonged electrolysis of \( H_{2} O \)
4. All of these

Answer: Prolonged electrolysis of \( H_{2} O \)

Heavy water is deuterium oxide, so it is obtained by enriching water in deuterium. Prolonged electrolysis preferentially removes ordinary hydrogen, gradually increasing the concentration of heavy water.

Q3. The catalyst used in preparation of oxygen from hydrogen peroxide is:

1. manganese dioxide
2. magnesium oxide
3. manganese oxide
4. manganese sulphate

Answer: manganese dioxide

Manganese dioxide catalyzes the decomposition of hydrogen peroxide into water and oxygen without being consumed. It is the standard catalyst used in laboratory preparation of oxygen from H2O2.

Q4. Wilkinson's catalyst \( \left[R h\left(P h_{3} P\right)_{3} C l\right] \) is used for:

1. hydrogenation of oils
2. hydrogenation of alkynes
3. hydrogenation of alkenes
4. polymerisation of alkenes

Answer: hydrogenation of alkenes

Wilkinson's catalyst, Rh(PPh3)3Cl, is a classic homogeneous hydrogenation catalyst. It is especially used to hydrogenate alkenes to alkanes by adding hydrogen across carbon–carbon double bonds.

Q5. Which of the following option best describe the hydrogen economy?

1. Using dihydrogen in an efficient manner
2. Dihydrogen is carried and stored in the form of liquid or gas
3. Addition of dihydrogen to the reactant
4. Both (a) and (b)

Answer: Both (a) and (b)

The hydrogen economy refers to a system where hydrogen is produced, stored, transported, and used efficiently as an energy carrier. It also involves carrying and storing hydrogen in practical forms such as compressed gas or liquid hydrogen, so both (a) and (b) fit.

Q6. Which of the following is absorbed by H2SO4 in the given reaction?

1. HCOOH
2. CO
3. H2O
4. None of these

Answer: H2O

H2SO4 is a strong dehydrating agent and readily absorbs water (H2O) from its surroundings or reactions.

Q7. Water gas is produced by:

1. Passing steam through a red hot coke bed
2. Saturating hydrogen with moisture
3. Mixing oxygen and hydrogen in the ratio of 1:2
4. Heating a mixture of CO2 and CH4 in petroleum refineries

Answer: Passing steam through a red hot coke bed

Water gas is produced by passing steam over red hot coke, which results in a mixture of carbon monoxide (CO) and hydrogen (H2).

Q8. Which one of the following molecular hydrides acts as a Lewis acid?

1. NH3
2. H2O
3. B2H6
4. CH4

Answer: B2H6

B2H6 (diborane) acts as a Lewis acid because it has electron-deficient boron atoms that can accept electron pairs. The other options are not electron-deficient and do not exhibit Lewis acid behavior.

Q9. Which of the following statements about hydrogen is incorrect?

1. hydrogen has three isotopes of which tritium is the most common.
2. Hydrogen never acts as cation in ionic salts.
3. Hydronium ion, H3O+ exists freely in solution.
4. Dihydrogen does not act as a reducing agent.

Answer: hydrogen has three isotopes of which tritium is the most common.

The incorrect statement is A because tritium is the least common isotope of hydrogen, not the most common. Protium is the most abundant isotope of hydrogen.

Q10. Some statements about heavy water are given below: (a) Heavy water is used as a moderator in nuclear reactors. (b) Heavy water is more associated than ordinary water. (c) Heavy water is more effective solvent than ordinary water. Which of the above statements are correct?

1. (a) (a) and (c)
2. (b) (a) and (b)
3. (c) (a), (b) and (c)
4. (d) (b) and (c)

Answer: (b) (a) and (b)

Heavy water (D₂O) is used as a moderator in nuclear reactors due to its ability to slow down neutrons. It is also more associated than ordinary water because of stronger hydrogen bonding. However, it is not a more effective solvent than ordinary water.

Q11. The method used to remove temporary hardness of water is:

1. Calgon’s method
2. Clark’s method
3. Ion-exchange method
4. Synthetic resins method

Answer: Clark’s method

Clark's method involves adding calcium hydroxide to remove temporary hardness caused by bicarbonates of calcium and magnesium.

Q12. Which of the following groups of ions makes the water hard?

1. (a) Sodium and bicarbonate
2. (b) Magnesium and chloride
3. (c) Potassium and sulphate
4. (d) Ammonium and chloride

Answer: (b) Magnesium and chloride

Hardness of water is caused by the presence of divalent cations like magnesium (Mg²⁺) and calcium (Ca²⁺). Among the options, magnesium and chloride contribute to water hardness.

Q13. The volume strength of 1.5 N H2O2 solution is

1. (a) 4.8L
2. (b) 52L
3. (c) 84L
4. (d) 88L

Answer: (c) 84L

Volume strength of H2O2 is calculated using the formula: Volume strength = Normality × 5.6. Substituting 1.5 N, we get 1.5 × 5.6 = 8.4 L, which matches option (c).

Q14. When H2O2 is oxidised, the product is

1. (a) OH−
2. (b) O2
3. (c) O2−
4. (d) HO2−

Answer: (b) O2

When H2O2 is oxidized, it loses electrons and forms molecular oxygen (O2) as the product. This is a well-known reaction of hydrogen peroxide in its role as a reducing agent.

Q15. Which of the following is the true structure of H2O2?

1. (a) H–O–O–H
2. (b) O–O | | H H
3. (c) H | H–O = O
4. (d) H | H–O < O

Answer: (b) O–O | | H H

The correct structure of H2O2 is a non-planar structure with an O–O single bond and two hydroxyl groups attached to the oxygen atoms, represented as H–O–O–H.

Q16. The O–O–H bond angle in H2O2 is

1. (a) 106°
2. (b) 109° 28′
3. (c) 120°
4. (d) 97°

Answer: (d) 97°

The O–O–H bond angle in H2O2 is approximately 97° due to the repulsion between lone pairs on oxygen atoms and the bent structure of the molecule.

Q17. Match the following and identify the correct option.

1. (A) CO(g) + H2(g) (i) Mg(HCO3)2 + Ca(HCO3)2
2. (B) Temporary hardness of water (ii) An electron deficient hydride
3. (C) B2H6 (iii) Synthesis gas
4. (D) H2O2 (iv) Non-planar structure

Answer: (C) B2H6 (iii) Synthesis gas

The correct matches are: (A) - (iii) as CO and H2 form synthesis gas, (B) - (i) as temporary hardness is due to bicarbonates, (C) - (ii) as B2H6 is an electron-deficient hydride, and (D) - (iv) as H2O2 has a non-planar structure.

Q18. Pure nitrogen is prepared in the laboratory by heating a mixture of

1. NH4OH + NaCl
2. NH4NO3 + NaCl
3. NH4Cl + NaOH
4. NH4Cl + NaNO2

Answer: NH4Cl + NaNO2

Pure nitrogen is prepared in the laboratory by heating a mixture of ammonium chloride (NH4Cl) and sodium nitrite (NaNO2), which react to produce nitrogen gas, water, and sodium chloride.

Q19. Of the following hydrides which one has the lowest boiling point?

1. ASH3
2. SbH3
3. PH3
4. NH3

Answer: PH3

PH3 has the lowest boiling point because it lacks strong hydrogen bonding, unlike NH3, and is lighter than SbH3 and AsH3, which have higher molecular weights.

Q20. HI can be prepared by all the following methods, except

1. (a) PI₃ + H₂O
2. (b) KI + H₂SO₄
3. (c) I₂ + H₂ → Pt →
4. (d) I₂ + H₂S

Answer: (b) KI + H₂SO₄

HI cannot be prepared by reacting KI with H₂SO₄ because H₂SO₄ oxidizes HI to I₂, preventing its isolation. The other methods are valid for HI preparation.