Question 1

Which of the following is NOT an isotope of hydrogen?

Accepted Answer

Helium is a separate element (atomic number 2); protium, deuterium, and tritium are the three naturally occurring isotopes of hydrogen.

Question 2

In the reaction 2H₂ + O₂ → 2H₂O, how many moles of water are produced from 4 moles of hydrogen gas?

Accepted Answer

From the balanced equation, 2 moles of H₂ produce 2 moles of H₂O; therefore, 4 moles of H₂ produce 4 moles of H₂O.

Question 3

Which position does hydrogen occupy in the periodic table?

Accepted Answer

Hydrogen is placed in Group 1 (alkali metals group) and Period 1 as the first element in the periodic table.

Question 4

What is the oxidation state of hydrogen in the compound H₂O₂ (hydrogen peroxide)?

Accepted Answer

In H₂O₂, oxygen has an oxidation state of -1 (peroxide ion), making hydrogen +1 to balance the molecule.

Question 5

What is the atomic number of hydrogen?

Accepted Answer

Hydrogen is the lightest element with atomic number 1 and one proton.

Question 6

Which reaction correctly represents the preparation of hydrogen gas in the laboratory using a dilute acid?

Accepted Answer

Zinc is sufficiently reactive to displace hydrogen from dilute HCl; copper and silver cannot displace hydrogen.

Question 7

The bond dissociation energy of H₂ molecule is approximately 436 kJ/mol. What does this value indicate?

Accepted Answer

Bond dissociation energy is defined as the energy required to break one mole of bonds in a gaseous molecule.

Question 8

In which oxidation state does hydrogen exist in the compound H₂O₂ (hydrogen peroxide)?

Accepted Answer

In H₂O₂, oxygen has oxidation state -1 (peroxide state), making hydrogen +1 to balance the molecule.

Question 9

What is the electron configuration of hydrogen in its ground state?

Accepted Answer

Hydrogen has only one electron, which occupies the 1s orbital in its ground state.

Question 10

Which isotope of hydrogen contains one proton and one neutron?

Accepted Answer

Deuterium (²H or D) has one proton and one neutron, while protium has no neutrons and tritium has two neutrons.

Question 11

In the reaction 2H₂ + O₂ → 2H₂O, how many grams of hydrogen are needed to produce 18 grams of water?

Accepted Answer

Molar mass of H₂O is 18 g/mol; 18 g = 1 mol H₂O requires 2 g H₂ (molar mass 2 g/mol) from stoichiometry.

Question 12

Which of the following best describes the position of hydrogen in the periodic table?

Accepted Answer

Hydrogen's unique electronic structure allows it to be classified with alkali metals (Group 1), halogens (Group 17), or separately.

Question 13

What is the oxidation state of hydrogen in the compound NaH (sodium hydride)?

Accepted Answer

In metal hydrides like NaH, hydrogen acts as a hydride ion (H⁻) with oxidation state -1.

Question 14

The ionization enthalpy of hydrogen atom is 13.6 eV. Which of the following statements about hydrogen is correct in relation to this value?

Accepted Answer

Hydrogen's ionization enthalpy (13.6 eV) is relatively high and comparable to halogens, enabling it to form stable covalent bonds with non-metals rather than ionizing easily.

Question 15

When hydrogen gas is passed over heated copper oxide, the following reaction occurs: CuO + H₂ → Cu + H₂O. Based on this reaction, which property of hydrogen is being demonstrated?

Accepted Answer

In this reaction, hydrogen is oxidized from 0 to +1 oxidation state while reducing Cu²⁺ to Cu⁰, demonstrating its reducing agent property.

Question 16

At standard temperature and pressure, hydrogen exists as diatomic H₂ molecules with a bond dissociation energy of approximately 436 kJ/mol. Which of the following correctly explains why hydrogen does NOT readily exist as monatomic H atoms under normal conditions?

Accepted Answer

The H-H bond dissociation energy of 436 kJ/mol is sufficiently high that thermal energy at standard conditions cannot break the bond, keeping hydrogen in its stable diatomic form.

CAPF AC Hydrogen

Hydrogen — Practice Questions