3: Solubility

The stated data directly give the amount of solute dissolved per 100 grams of solvent: 10 grams solute per 100 grams water. This is a valid mass-based expression of solubility at the stated temperature, even though textbooks may use other standard bases in particular contexts. The other options use unrelated substances or physical units, so A is correct.

An unsaturated solution contains less dissolved solute than the maximum amount possible at that temperature and for that amount of solvent. Therefore, more solute can still dissolve. A saturated solution has reached the normal limit, while a supersaturated solution exceeds it under special metastable conditions. Thus A precisely answers the question.

The solubility statement already uses the same solvent amount asked about: 40 grams of solute per 100 grams of water. Therefore, at the specified temperature, 100 grams of water can dissolve a maximum of 40 grams of the solute. No scaling is needed. The other numbers result from incorrect multiplication or addition, so A is correct.

Solubility is given as 20 g of solute for every 100 g of water. For 50 g of water, use a direct proportion: solute mass = 20 × 50/100 = 10 g. Therefore, at the stated temperature, a maximum of 10 g can dissolve to form a saturated solution. The values 20 g, 40 g, and 100 g would correspond to incorrect scaling of the water amount, so option A is correct.

The solubility ratio is 25 g solute : 100 g water. Since 200 g water is twice 100 g, the amount of solute required for saturation is also twice 25 g: 25 × 200/100 = 50 g. This calculation assumes the temperature remains the same and that the solute and solvent amounts are measured consistently. Hence option A is correct; 25 g would apply to only 100 g of water.

For 100 grams of water, the maximum amount that can dissolve at the stated temperature is 40 grams. Only 30 grams is present in solution, so it is 10 grams below the saturation limit and can accept more solute. It is therefore unsaturated. Equal amounts would indicate saturation, while a stable excess is not implied here. A is correct.

At the stated temperature, 40 grams is the maximum amount that can dissolve in 100 grams of water. The solution contains exactly this amount, so it has reached its solubility limit and is saturated. It is not unsaturated because no further amount is specified as dissolvable, and it is not pure solvent or merely a suspension. Thus A is correct.

At the stated temperature, 40 grams is the ordinary saturation limit for 100 grams of water. If 45 grams is genuinely dissolved, the solution contains more solute than the normal limit and is therefore supersaturated. Such a condition is generally metastable and may crystallize when disturbed. It is not unsaturated or pure water, so A is correct.

Carbon dioxide is more soluble in a liquid when its partial pressure above the liquid is high. Beverage manufacturers therefore carbonate drinks under pressure and seal them to maintain that pressure. Opening the cap lowers the pressure and allows CO2 to escape as bubbles. Strong sunlight is not the governing condition. Hence A is correct.

At constant temperature, Henry’s law gives a direct relationship between a gas’s partial pressure and its solubility in a liquid. When the pressure above the liquid decreases, the equilibrium amount of dissolved gas also decreases, and some gas may come out of solution as bubbles. Thus, option A is correct. Lower pressure does not make solubility unlimited, and terms such as “becomes hard” do not describe a solution property.

Common salt is an ionic substance, and water is a polar solvent that can hydrate and stabilize its ions. Consequently, a considerable amount dissolves in water. Sand, wax, and oil are poorly soluble or effectively immiscible in water under ordinary conditions. “Highly soluble” is a comparative classroom description here, so A is the best answer.

Sand is composed mainly of silica and other mineral particles that do not interact favorably enough with polar water to dissolve appreciably. It therefore remains as solid particles and may settle. Sugar and salt dissolve much more readily, while a small amount of oxygen can dissolve as a gas. Thus, among the options, sand has very low solubility and A is correct.

A substance is called insoluble in a particular solvent when it does not dissolve, or dissolves only to a negligible extent, under the stated conditions. The term is relative to the solvent and conditions. Saturated describes a solution’s capacity, molar describes concentration, and volatile describes ease of vaporization. Therefore A is the correct term.

Solubility is often temperature-dependent: most solids become more soluble on heating, while gases generally become less soluble. Therefore, two numerical values cannot be compared fairly unless their temperatures are the same or explicitly known. Temperature does not change the name of a substance or always change its colour. Hence A gives the correct reason.

Gas particles are separated by large spaces, so gases can be compressed considerably and their pressure can change substantially. Increasing the partial pressure increases the frequency with which gas molecules enter the liquid, raising solubility. Solids and liquids are much less compressible. The other statements deny basic particle theory, so A is correct.

For most solid solutes, increasing temperature increases solubility because the dissolution process is commonly endothermic or otherwise favored by heating. Thus more solute can dissolve in a fixed amount of solvent. This is a general trend and has exceptions. Pressure removal, container paint, and clock changes do not generally increase solid solubility, so A is correct.

At constant composition, gas solubility generally rises with increasing pressure and falls with increasing temperature. Therefore, high pressure pushes more gas into the liquid, while low temperature reduces its tendency to escape. The combination in A uses both favorable changes. Low pressure, high temperature, zero conditions, or removing the solvent cannot increase useful gas solubility.

Boiling raises the temperature of water substantially. Gas solubility in a liquid generally decreases as temperature rises, and vigorous motion during boiling helps dissolved gas molecules leave the liquid and enter the atmosphere. Consequently, boiled water contains less dissolved gas after cooling unless it is exposed to air again. The gases do not become solids or salts, and they cannot make water metallic, so option A is correct.

Ionic solutes interact favorably with polar solvents because the solvent’s partial charges attract and stabilize the ions. Water is a common polar solvent, so this pairing follows the idea of similar or compatible intermolecular forces. Oil and wax are largely non-polar, while sand is not appreciably soluble in water. Thus A is the best pair.

“Sparingly soluble” means that only a small amount of a substance dissolves in the specified solvent under stated conditions. It does not necessarily mean absolutely insoluble; a tiny measurable amount may dissolve. “Highly boiling,” “shiny,” and “fully gaseous” describe different properties and do not express low solubility. Therefore A is correct.

A saturated solution contains the maximum amount of solute that can dissolve at its current temperature. For many solids, heating increases solubility, so the previous solution can dissolve additional solute and becomes unsaturated relative to the new temperature. This is not universal for every solid, but it is the usual trend. Thus A is correct.

The statement is incorrect because different substances have different structures, polarities, and intermolecular forces. Consequently, their solubilities in water vary widely: some dissolve readily, some dissolve only slightly, and others are nearly insoluble. Solubility also depends on temperature and sometimes pressure. Therefore A is correct, while the other descriptions do not evaluate the scientific statement.

Solubility is an equilibrium property: it indicates the maximum amount of solute that can dissolve in a given amount of solvent at specified conditions. Rate of dissolving is a kinetic property: it indicates how quickly the process occurs. Stirring or grinding can increase rate without necessarily changing final solubility. Hence A correctly distinguishes them.

At a fixed temperature, undissolved solute remaining at the bottom usually indicates that the liquid has reached its dissolving capacity. The dissolved portion and excess solid can coexist in equilibrium, so the solution is saturated. This conclusion assumes the solid is in contact with the solution and enough time has allowed equilibrium. Therefore A is correct.

A sound first step is to identify the temperature, pressure, and chemical nature of the solute and solvent. Temperature often controls solid or gas solubility, pressure is especially important for gases, and polarity or intermolecular forces determine compatibility. These clues guide the concept or calculation. Pen colour, question length, and page number have no scientific relevance.