3: Solubility

Correct answer: A. Solubility

Explanation: Solubility is the maximum amount of a solute that can dissolve in a specified amount of solvent at a particular temperature, usually producing a saturated solution. For a solid in a liquid, it may change with temperature and with the nature of both substances. Vapour pressure, density and viscosity describe different physical properties, so solubility is option A.

Correct answer: B. Saturated solution

Explanation: A saturated solution contains the maximum amount of solute that can dissolve in a given amount of solvent at a specified temperature. If additional solute is added, it remains undissolved or establishes dynamic equilibrium with the solution. Unsaturated means more solute can dissolve, while dilute and concentrated only describe relative amount, not necessarily the solubility limit. Therefore B is correct.

Correct answer: C. Unsaturated solution

Explanation: An unsaturated solution contains less solute than the maximum amount that can dissolve at the stated temperature, so additional solute can still dissolve. A saturated solution has reached its normal solubility limit, while a supersaturated solution contains more dissolved solute than that limit and is unstable. A colloidal solution is classified by particle size, not by this capacity. Therefore C is correct.

Correct answer: A. It increases

Explanation: For most solid solutes, dissolution becomes more favourable as temperature rises, often because the dissolving process absorbs heat. Therefore, a higher temperature generally permits a larger amount of the solid to dissolve in a fixed amount of water. This is a general trend, not an absolute rule: some solids show little change or even decreased solubility. Thus, option A is correct, while the words “always,” “zero,” and “decreases” are not generally valid.

Correct answer: A. It decreases

Explanation: The dissolution of a gas in a liquid is generally an exothermic process. When the liquid is heated, the increased molecular motion makes dissolved gas molecules leave the liquid more easily, so gas solubility usually decreases. This is why warm water holds less oxygen than cool water. The trend is general rather than universal, but among the given choices, decrease is the scientifically appropriate answer; the other options have no basis.

Correct answer: A. Solubility increases

Explanation: At constant temperature, increasing the pressure of a gas above a liquid increases the gas concentration at the liquid surface and favours its entry into the liquid. Henry’s law expresses this as solubility being proportional to the gas’s partial pressure, within the law’s applicable range. Consequently, more gas dissolves at higher pressure. Therefore, option A is correct; increased pressure does not make solubility zero or prevent dissolution.

Correct answer: A. Solubility of a gas in a liquid

Explanation: Henry’s law describes the behaviour of a gas dissolved in a liquid. At a fixed temperature and for suitable dilute conditions, the concentration or solubility of the gas is related directly to its partial pressure above the solution. This principle explains why carbonated drinks retain more carbon dioxide under pressure. Melting point, acid strength, and metallic lustre are different properties and are not the subject of Henry’s law, so option A is correct.

Correct answer: A. The partial pressure of the gas

Explanation: Henry’s law states that, at constant temperature and within its applicable concentration range, the amount or concentration of a gas dissolved in a liquid is proportional to the gas’s partial pressure above the liquid. Thus, doubling the relevant partial pressure generally increases the dissolved amount in the same proportion. Solvent colour, container shape, and clock time do not determine this relationship, so option A is correct.

Correct answer: A. Dissolved gas comes out due to pressure decrease

Explanation: Carbon dioxide is bottled under pressure, which keeps a relatively large amount dissolved in the drink. Opening the bottle suddenly lowers the pressure above the liquid. The equilibrium then shifts toward escaping CO2, producing bubbles. No freezing, burning of sugar, or instant vaporization of water is required, so A is correct.

Correct answer: A. Pressure is higher

Explanation: Hydrostatic pressure increases as depth increases because a deeper point supports a taller column of water. Higher pressure generally increases the solubility of gases in a liquid, as described by Henry’s law, so more gas can remain dissolved at depth. Temperature and salinity also influence actual ocean solubility, but the pressure-based reason asked here is the higher pressure. Therefore, option A is correct; the other statements are false.

Correct answer: A. Temperature

Explanation: Solubility is influenced by the nature of the solute and solvent and by conditions such as temperature; for gases, pressure is also especially important. Temperature can change the equilibrium between dissolving and escaping. The colour of paper, sound, and table height have no chemical role in solubility. Hence A is the only relevant option.

Correct answer: A. Very little effect

Explanation: Solids and liquids are nearly incompressible, so changing pressure usually produces only a very small change in their volumes and solubilities. Pressure has a much clearer effect on gases because gases are highly compressible. Thus A is correct. The other options incorrectly claim a huge effect, zero solubility, or conversion of the solid into a gas.

Correct answer: A. Polar solute dissolves better in polar solvent

Explanation: The phrase “like dissolves like” means that substances with similar intermolecular forces tend to mix more easily. Polar or ionic solutes generally interact favorably with polar solvents, while non-polar solutes are better suited to non-polar solvents. It is not an absolute rule for every substance, but A expresses the intended principle correctly.

Correct answer: A. Because water is a polar solvent

Explanation: Common salt, mainly sodium chloride, is an ionic solid. Water has polar molecules whose partial charges attract Na+ and Cl− ions and help separate them from the crystal lattice. Hydration then stabilizes the separated ions in solution. Water is not non-polar, and salt is neither wax nor a gas, so A is correct.

Correct answer: A. Non-polar

Explanation: Water is strongly polar, whereas most oils consist mainly of non-polar hydrocarbon molecules. The interactions between oil and water are not favorable enough to mix them extensively, so they form separate layers. Oil is not an ionic electrolyte in this context. Therefore, the non-polar description in A correctly explains its poor solubility.

Correct answer: A. Some solute may separate as crystals

Explanation: If a hot solution contains more dissolved solute than can remain dissolved at a lower temperature, cooling reduces the solubility. The excess solute then separates from the solution, often as crystals, provided suitable crystallization conditions exist. Cooling does not make all solvent disappear or convert the solute into metal. Thus A is correct.

Correct answer: A. It contains more solute than the normal limit

Explanation: At a specified temperature, a supersaturated solution contains more dissolved solute than the amount present in an ordinary saturated solution. It is usually prepared by dissolving extra solute at a higher temperature and cooling carefully. Such a state is metastable, so a seed crystal or disturbance may cause crystallization. Hence A is correct.

Correct answer: A. Low temperature and high pressure

Explanation: Gas solubility generally increases when pressure is raised and decreases when temperature is raised. Therefore, combining high pressure with low temperature favors retention of the gas in the liquid and gives the greatest solubility among the listed choices. The other combinations include either low pressure or high temperature, both unfavorable for gas dissolution.

Correct answer: A. For respiration

Explanation: Fish obtain oxygen from the water through their gills. The dissolved oxygen is used in cellular respiration to release energy from food for movement, growth, and maintenance. Fish cannot normally use the hydrogen and oxygen atoms of water as a substitute for respiratory oxygen. Colour change, freezing, and salt formation are unrelated, so A is correct.

Correct answer: A. Gas solubility decreases in warm water

Explanation: Heating generally decreases the solubility of gases in water, so oxygen escapes more readily and the concentration of dissolved oxygen falls. If oxygen consumption by aquatic organisms is high, this reduction can create stress or shortage for fish. Water does not vanish merely because it is warm, and the other options do not explain the effect. A is correct.

Correct answer: A. Nature of solute and solvent

Explanation: The value of solubility depends strongly on the chemical nature of both substances: polarity, intermolecular forces, and possible chemical interaction affect how much dissolves. Temperature and, for gases, pressure also matter. Container brightness, handwriting, and the name of the day have no chemical influence, so A identifies the relevant factor.

Correct answer: A. Saturated state

Explanation: When a solution is in equilibrium with excess undissolved solute at a fixed temperature, it has reached its maximum dissolving capacity and is saturated. The solid may remain at the bottom because additional solute cannot dissolve under those conditions. The other options do not describe a solution containing dissolved solute and residue. Therefore A is correct.

Correct answer: A. Rate of dissolving increases

Explanation: Stirring continually brings fresh solvent into contact with the sugar surface and carries dissolved sugar away from that surface. This increases the rate at which sugar dissolves. At a fixed temperature, however, stirring does not necessarily change the final equilibrium solubility or maximum amount that can dissolve. Thus A is correct and B is too absolute.

Correct answer: A. Surface area is larger

Explanation: For the same total mass, powdered sugar exposes a much larger total surface area to water than one large piece. More water molecules can contact the solid simultaneously, so the rate of dissolution increases. This changes the speed, not necessarily the equilibrium solubility at a fixed temperature. Therefore A is correct; the other options are chemically irrelevant or false.

Correct answer: A. Fixed amount of solvent

Explanation: Solubility is reported as the amount of solute that dissolves in a specified amount of solvent at a specified temperature. A fixed solvent mass or volume provides a meaningful basis for comparison between substances and experiments. Classroom length, chalk colour, and book page number have no role in defining solubility. Hence A is correct.