Q.The colligative property of a solution is
a. vapour pressure
b. boiling point
c. osmotic pressure
d. freezing point

Colligative properties depend only on the NUMBER of solute particles, not their identity. "Freezing point" as stated is not itself such a property.

A colligative property is one whose magnitude depends only on the number (mole fraction/molality) of solute particles present in a solution, and not on their chemical nature. The four classical colligative properties are: relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, and osmotic pressure.

Looking at the options: (a) elevation of boiling point, (b) lowering of vapour pressure, and (c) osmotic pressure are each, by name, directly one of the four colligative properties. Option (d) says simply "freezing point" — this is the actual temperature at which the solid and liquid phases are in equilibrium, an intrinsic physical constant of the substance. It is the CHANGE in freezing point (depression, ΔTf = Kf·m) on adding a solute that is colligative, not the freezing point value itself.

Osmotic pressure is a colligative property because it depends only on the number of solute particles dissolved, not their chemical identity.

Colligative properties are physical properties of a solution that depend only on the number of solute particles present, not on their nature. The four classical colligative properties are: (1) relative lowering of vapour pressure, (2) elevation in boiling point, (3) depression in freezing point, and (4) osmotic pressure.

Among the given options, "vapour pressure" and "boiling point" themselves are ordinary properties of a solution, not colligative properties — it is the lowering of vapour pressure and the elevation of boiling point on adding a solute that are colligative. Osmotic pressure, however, is itself a colligative property: for a dilute solution, $\pi = CRT$, where $C$ is the molar concentration of solute particles, $R$ is the gas constant and $T$ is the temperature — $\pi$ depends only on the number of solute particles present.

$\Delta T_b$, $\Delta T_f$ and $\pi$ are colligative properties (they depend on the number of solute particles); $K_b$ is a solvent-specific constant that relates them, not a property itself.

Colligative properties depend only on the number of solute particles present in a solution, not their chemical identity. The four classical colligative properties are: relative lowering of vapour pressure, elevation in boiling point ($\Delta T_b$), depression in freezing point ($\Delta T_f$), and osmotic pressure ($\pi$).

$K_b$ (the molal elevation/ebullioscopic constant) is the proportionality constant in $\Delta T_b = K_b \cdot m$. It is a characteristic of the solvent (related to its molar mass and latent heat of vaporization) and stays fixed for a given solvent regardless of the solute — so it is not a colligative property, unlike $\Delta T_b$, $\Delta T_f$, and $\pi$ which change with solute concentration.

Colligative properties are defined precisely as properties that depend on the number of solute particles in solution, not on what those particles are — so option (b) is correct by definition.

The defining feature of colligative properties

Colligative properties — relative lowering of vapour pressure, elevation in boiling point ($\Delta T_b$), depression in freezing point ($\Delta T_f$), and osmotic pressure ($\pi$) — arise purely from the dilution effect a solute has on the solvent: adding solute particles lowers the effective mole fraction/chemical potential of solvent molecules at the surface, which shifts vapour–liquid and solid–liquid equilibria. This shift depends only on how many solute particles are present per unit amount of solvent, e.g. $\pi = CRT$ or $\Delta T_b = K_b\,m$, where $C$ (or molality $m$) counts particles, with no term for the solute's identity, mass, or specific charge (beyond the van't Hoff factor $i$, which itself just corrects the particle count for dissociation/association).

Why the other options fail: (a) and (d) are wrong because the whole point of a colligative property is that it is independent of the chemical nature of the solute (or solvent) — two different solutes at the same molar concentration produce the same $\Delta T_b$, $\Delta T_f$, or $\pi$ (ignoring dissociation effects). (c) is wrong because it is the solute particle count relative to solvent, not the number of solvent particles alone, that determines the effect.

Colligative properties depend on the ratio of the number of solute particles to the number of solvent molecules in the solution.

Colligative properties (relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, osmotic pressure) depend only on the number of solute particles present in a given amount of solvent (i.e. on molar concentration/mole fraction of solute), and are independent of the chemical identity or nature of the solute particles.

Colligative properties are a set of solution properties that depend solely on the number of dissolved solute particles relative to the total number of solvent molecules, regardless of what the solute chemically is.

When a non-volatile solute is dissolved in a solvent, several physical properties of the resulting solution change in a way that depends only on the ratio of the number of solute particles to solvent molecules — not on the size, mass, or chemical identity of the solute particles. Such properties are called colligative properties (from Latin colligatus, meaning 'bound together').

The four classical colligative properties are:

1. Relative lowering of vapour pressure, $\dfrac{p^0 - p_s}{p^0} = x_2$
2. Elevation of boiling point, $\Delta T_b = K_b\, m$
3. Depression of freezing point, $\Delta T_f = K_f\, m$
4. Osmotic pressure, $\pi = CRT$

These are widely used to determine the molar mass of an unknown solute.

Colligative properties (relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, osmotic pressure) depend solely on how many solute particles are present per unit of solvent, never on what the particles chemically are.

Colligative properties arise because dissolved solute particles physically get in the way of solvent molecules (lowering the escaping tendency of the solvent), so their magnitude depends only on the ratio of solute particles to solvent particles/moles present, not on the size, mass, or chemical nature of those particles. This is why equimolal solutions of glucose and urea — two chemically very different non-electrolytes — show identical elevation of boiling point and identical osmotic pressure: both contribute exactly one particle per formula unit.

Options (a), (c) and (d) all try to tie the property to the identity (nature) of the solute or solvent, which is exactly what colligative properties are defined to be independent of. This is also why a dissociating electrolyte (e.g., $NaCl \rightarrow Na^+ + Cl^-$) shows a larger colligative effect than a non-electrolyte of the same molal concentration — because it produces more particles, not because Na$^+$/Cl$^-$ are chemically special (captured by the van't Hoff factor $i$).

Colligative properties depend only on the number of solute particles, not their identity. Of the four options, only "elevation in boiling point" correctly names one.

Colligative properties are properties of a solution that depend on the number of solute particles present, not on their chemical nature. The four true colligative properties are:

1. Relative lowering of vapour pressure
2. Elevation in boiling point ($\Delta T_b$) — a non-volatile solute raises the boiling point of the solvent
3. Depression in freezing point ($\Delta T_f$) — a non-volatile solute lowers the freezing point of the solvent
4. Osmotic pressure

Looking at the given options: "Elevation in freezing point" (option a) and "Depression in boiling point" (option c) describe the wrong direction of change — freezing point is depressed, not elevated, and boiling point is elevated, not depressed, when a non-volatile solute is added. Only option (b), "Elevation in boiling point," correctly names a real colligative property, so "All of the above" (option d) is not correct since two of the three listed phenomena are mis-stated.

Colligative properties (relative lowering of vapour pressure, boiling-point elevation, freezing-point depression, osmotic pressure) depend purely on the count of solute particles per unit amount of solvent, never on what the particles chemically are.

By definition, a colligative property changes in direct proportion to the number of solute particles (molecules or ions) present in a given amount of solvent, regardless of their size, shape, mass, or chemical nature. This is why, for example, a mole of glucose and a mole of urea (unequal molar masses, totally different chemistry) produce the same boiling-point elevation in the same solvent — but an electrolyte that dissociates into 2 or 3 ions shows a proportionally larger effect (captured via the van't Hoff factor $i$), precisely because it increases the number of particles.