NEET Chemistry: Atomic and molecular masses Practice Questions

Correct answer: A — 35

Mass Number (A) = Number of Protons + Number of Neutrons = 17 + 18 = 35.

Correct answer: B — The isotope with the smallest mass

The most stable isotope is generally the one with the configuration that minimizes the repulsive forces, which often correlates with a balanced ratio of protons and neutrons. In the context of general mass stability, the option emphasizing minimum mass often relates to the nucleus configuration for certain elements, though stability depends on the specific nuclide.

Correct answer: D — atomic mass unit (amu or u)

The atomic mass unit (amu or u) is the standard unit used to express the mass of individual atoms and relative atomic masses.

Correct answer: C — Law of Conservation of Mass

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction, meaning the total mass of reactants equals the total mass of products.

Correct answer: C — The difference between the theoretical mass and the actual measured mass

Mass defect is the difference between the expected mass calculated from the masses of the separate nucleons (protons and neutrons) and the actual measured mass of the nucleus. This mass difference is converted into energy (mass defect = E=mc²).

Correct answer: B — Atomic number

The mass of an atom is expressed in atomic mass units (amu). The atomic mass unit (amu) is the unit used to measure the mass of individual atoms and molecules.

Correct answer: A — Isotopes

Atoms of the same element having different numbers of neutrons are defined as isotopes.

Correct answer: D — Gram

The kilogram (kg) is the SI unit for mass. While the gram (g) is commonly used, the kilogram is the base unit, and mass is measured in kilograms.

Correct answer: A — 18 g

The molar mass of water is calculated by summing the atomic masses: (2 * 1.0) + 16.0 = 18.0. Therefore, one mole of water has a mass of 18 g.

Correct answer: D — 6.022 × 10²³ molecules

One mole is defined as 6.022 × 10²³ elementary entities (atoms, molecules, ions, etc.), as defined by Avogadro's number (N_A).

Correct answer: A — Atomic Number

The Atomic Number (Z) is defined as the number of protons in the nucleus of an atom.

Correct answer: A — Isotopic mass ratio

The isotopic mass ratio (the ratio of the masses of two isotopes) is a dimensionless quantity used for comparison, which is fundamental when discussing isotopic masses.

Correct answer: A — Atomic Mass Unit (amu or u)

Atomic mass is expressed in atomic mass units (amu or u). This unit is defined based on the mass of a specific isotope of carbon-12, making it the standard unit for atomic masses.

Correct answer: B — The total mass of all atoms present in one molecule of water.

Molecular mass is the sum of the masses of all the atoms present in the molecule. For H₂O, it is the sum of the masses of two hydrogen atoms and one oxygen atom.