Why Correct: Glass forms when a molten silica mixture cools too rapidly for crystals to form, resulting in an amorphous solid with liquid-like disordered molecular structure.
Distractor Analysis: Gels contain a continuous solid network with liquid trapped inside, like jelly. Alloys are homogeneous mixtures of metals, such as steel or brass. Eutectic mixtures have specific compositions that melt at a single temperature lower than any component alone, like solder.
Takeaway: Other amorphous solids include obsidian (volcanic glass) and many plastics, while crystalline solids like quartz have regular atomic arrangements.

Why Correct: Below the critical temperature, intermolecular attractive forces are strong enough to bind molecules into a liquid when pressure is applied. Compression brings molecules closer, allowing these forces to overcome kinetic energy.
Distractor Analysis: Finite size explains why gases are compressible but not liquefaction. Random motion opposes condensation. Spherical shape is irrelevant to phase change.
Takeaway: Critical temperature is the highest temperature at which a gas can be liquefied by pressure alone; above it, no amount of compression causes liquefaction.

Why Correct: Molecular weight equals twice the vapour density. With vapour density 32, molecular weight is 64 g/mol.
Distractor Analysis: 16 g/mol would correspond to methane (CH4) but is half of 32, not double. 32 g/mol is the vapour density itself, not the molecular weight. 128 g/mol is double of 64, which would require vapour density 64.
Takeaway: Molecular weight = 2 × Vapour density for any gas at same temperature and pressure; vapour density is measured relative to hydrogen.

Why Correct: 17 g NH3 equals exactly one mole (molar mass 17 g/mol), so at NTP it occupies 22.4 litres.
Distractor Analysis: 22 g CO2 is half a mole (molar mass 44 g/mol) and occupies 11.2 L. 1.7 g NH3 is 0.1 mole and occupies 2.24 L. 4.4 g CO2 is 0.1 mole and also occupies 2.24 L. None of these equal 22.4 L.
Takeaway: At NTP, the volume of a gas is directly proportional to the number of moles: V(L) = n × 22.4. Always compute moles = given mass / molar mass.

Why Correct: 14 g of N2 corresponds to 0.5 mol (molar mass 28 g/mol), so n = 0.5 × Avogadro's number. 46 g of NO2 corresponds to 1 mol (molar mass 46 g/mol), which contains Avogadro's number of molecules. Since Avogadro's number is twice 0.5 × Avogadro's number, the number of molecules in 46 g NO2 is 2n.
Distractor Analysis: n would be the count if the mass of NO2 were 23 g (0.5 mol). n/2 would be the count if the mass were 11.5 g (0.25 mol). 3n/2 would be the count if the mass were 34.5 g (0.75 mol).
Takeaway: The mole concept links mass to particle count via molar mass; 1 mol of any substance contains 6.022 × 10^23 entities, and the number of moles equals mass divided by molar mass.

Why Correct: Low pressure and high temperature minimize both intermolecular forces and the finite molecular volume, allowing the gas to follow the ideal gas equation PV = nRT. At low pressure, the average distance between molecules is large, so attractions are weak; at high temperature, molecular kinetic energy is high, so any residual attractions are easily overcome.
Distractor Analysis: High temperature and high pressure is incorrect because at high pressure, molecules are forced close together, making the finite molecular volume and intermolecular attractions significant, causing deviation from ideal behaviour. High pressure and low temperature is the most extreme deviation condition, where gases may liquefy and van der Waals forces dominate. Low pressure and low temperature is incorrect because at low temperature, the kinetic energy of molecules is low, making intermolecular attractions relatively more important, causing deviation from ideal behaviour.
Takeaway: The compressibility factor Z = PV/nRT equals 1 for an ideal gas; real gases show Z 1 at high pressure (repulsions and molecular volume dominate). At the Boyle temperature, a real gas behaves ideally over a wider pressure range.