NEET Chemistry: Some Basic Concepts in Chemistry Practice Questions

Correct answer: B — The molecular formula is a multiple of the empirical formula.

The molecular formula represents the actual number of molecules, and the empirical formula is the simplest ratio. Therefore, the molecular formula is always a whole-number multiple of the empirical formula.

Correct answer: C — 20%

The percentage composition of Oxygen is directly given as 20%.

Correct answer: C — Gas

In the gaseous state, particles move randomly and far apart, resulting in the weakest intermolecular forces compared to the ordered arrangement in solids and liquids.

Correct answer: C — Multiple ratios

The law of multiple proportions states that elements combine in simple whole number ratios by mass to form compounds.

Correct answer: B — Atoms combine in simple whole-number ratios

Dalton's theory assumes that atoms are neither created nor destroyed during a chemical reaction, only rearranged.

Correct answer: C — Law of Definite Proportions

The relationship between the masses of elements combining to form compounds is the basis for the Law of Multiple Proportions.

Correct answer: A — 2 moles

Moles can be calculated by dividing the given mass by the molar mass. Moles = Mass / Molar Mass = 36 g / 18 g/mol = 2 moles.

Correct answer: A — 6.022 × 10²³ mol

Avogadro's number (N_A) is the number of particles that make up one mole, meaning 1 mol of any substance contains 6.022 × 10²³ particles.

Correct answer: A — Mass of products

The Law of Conservation of Mass states that the total mass of the reactants must equal the total mass of the products in a closed system.

Correct answer: A — 35

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

Correct answer: D — Kilogram per cubic meter (kg/m³)

Density is defined as mass per unit volume. The SI unit for mass is kg, and for volume is m³, so the unit for density is kg/m³.

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: A — The mixture has uniform composition throughout the entire volume.

A homogeneous mixture (like salt dissolved in water) has a uniform composition throughout. In contrast, a heterogeneous mixture has non-uniform composition.

Correct answer: B — H₂O

Mass of H = 1; Mass of O = 2 * 16 = 32. The ratio of masses is 1:32. Dividing by the smallest mass (1) gives the ratio of moles. The empirical formula corresponds to 1 atom of H and 32/16 = 2 atoms of O, which gives H₂O.