NCERT Solutions Class 8 Science Chapter 9 2026-27 PDF

Concept used. A solution is a uniform mixture. Solubility of gases in water generally decreases on heating. Volume is space occupied, mass is amount of matter, and a saturated solution has reached its dissolving limit at that temperature. (i) F, (ii) F, (iii) F, (iv) F, (v) T.

1. (i) is false. Oxygen gas is more soluble in cold water than in hot water.
2. (ii) is false. Sand and water form a non-uniform mixture because sand does not dissolve evenly.
3. (iii) is false. The space occupied by an object is called volume. Mass means amount of matter.
4. (iv) is false. An unsaturated solution can dissolve more solute. A saturated solution has more solute dissolved up to its limit.
5. (v) is true. Air is a uniform mixture of gases, so it can be treated as a gaseous solution.

Concept used. Displacement measures volume from the rise in water level. Solubility is a maximum dissolving amount at a temperature. Heating usually increases volume without changing mass, so density decreases. (i) immersed, rise; (ii) solute, solvent; (iii) decreases; (iv) saturated.

1. In displacement, the solid object is immersed in water.
2. The water level rises, and this rise tells the object's volume.
3. Solubility is the maximum amount of solute that dissolves in a solvent at a particular temperature.
4. On heating, most substances expand. Their mass stays the same, so density generally decreases.
5. If no more glucose dissolves at that temperature, the solution is saturated.

Concept used. An object or liquid with lower density than water tends to float on water. Oil also does not dissolve in water in this observation. The correct option is (ii): water is denser than oil.

1. Oil stays above water, so oil has lower density than water.
2. If oil were denser than water, it would sink below the water.
3. If both had the same density, oil would not clearly form the top layer like this.
4. The observation also shows that oil does not dissolve uniformly in water.

Concept used. Density is mass divided by volume. Water has density close to 1 g/cm³, so a solid with density greater than water generally sinks in water. The density is 2.5 g/cm³. It will sink in water.

1. Use the formula Density=MassVolume.
2. Substitute the given values: Density=225 g90 cm³.
3. Calculate: 225÷ 90=2.5.
4. So the density of the stone sculpture is 2.5 g/cm³.
5. Since 2.5 g/cm³ is greater than the density of water, the sculpture will sink.

Concept used. A saturated solution has dissolved the maximum possible amount of solute at that temperature. An unsaturated solution can still dissolve more solute. The most appropriate statement is (iii).

1. Statement (iii) is correct because saturation means no more solute dissolves at that temperature.
2. Statement (i) is wrong because a saturated solution cannot dissolve more solute at the same temperature.
3. Statement (ii) is wrong because it describes a saturated solution, not an unsaturated solution.
4. Statement (iv) is wrong because saturated solutions can form at many temperatures. The limit depends on the solute, solvent and temperature.

Concept used. Capacity remaining equals total capacity minus volume already filled. Use the same unit before subtracting. The bottle can hold 1.5 litres more water, or 1500 mL.

1. Convert 2 litres to millilitres: 2 L=2000 mL.
2. Water already poured =500 mL.
3. Remaining capacity =2000 mL-500 mL=1500 mL.
4. Convert back if needed: 1500 mL=1.5 L.

Concept used. Density is the mass present in unit volume. Its value is obtained by dividing mass by volume. The density is 10 g/cm³.

1. Use Density=MassVolume.
2. Substitute: Density=400 g40 cm³.
3. Calculate: 40040=10.
4. So the density is 10 g/cm³.

Concept used. Floating depends on average density and the upward push of water. Orange peel contains air spaces and makes the whole unpeeled orange less dense than water. The unpeeled orange floats because its peel traps air and lowers its average density. The peeled orange sinks because removing the peel removes those air spaces and raises its average density.

1. The unpeeled orange includes the fruit plus the peel.
2. The peel has tiny air spaces and adds buoyancy.
3. Because of these air spaces, the average density of the unpeeled orange becomes less than water.
4. So the unpeeled orange floats.
5. When the peel is removed, many air spaces are removed too.
6. The peeled orange has higher average density than water, so it sinks.

Concept used. To compare density, calculate density for each object using mass divided by volume. The larger density value means the object is denser. Object A is denser. Its density is 5 g/cm³, while object B's density is 4 g/cm³.

1. For object A: Density=200 g40 cm³=5 g/cm³.
2. For object B: Density=240 g60 cm³=4 g/cm³.
3. Compare the two values: 5>4.
4. Therefore object A is denser than object B.

Concept used. Density depends on mass and volume, not on shape alone. If the same clay is reshaped without losing material or changing volume, its density remains unchanged. Its density remains the same, 2 g/cm³, if the mass and volume remain unchanged.

1. Initial mass of clay =120 g.
2. Initial volume =60 cm³.
3. Initial density =12060=2 g/cm³.
4. Flattening changes the shape from a cube to a sheet.
5. If no clay is lost and the volume remains the same, mass and volume do not change.
6. So the density remains 2 g/cm³.

Concept used. From Density=Mass/Volume, volume equals mass divided by density. The volume is about 75.95 cm³, or nearly 76 cm³.

1. Use Density=MassVolume.
2. Rearrange: Volume=MassDensity.
3. Substitute: Volume=600 g7.9 g/cm³.
4. Calculate: 6007.975.95.
5. So the volume is about 75.95 cm³.

Concept used. Heating water causes expansion. The mass of water remains almost the same, but its volume increases, so its density decreases. The density decreases because heating makes the water expand and rise in the glass tube.

1. The test tube contains water connected to a narrow glass tube.
2. When the test tube is placed in hot water, the water inside gets heated.
3. On heating, the water expands.
4. The expansion pushes the water level up in the glass tube.
5. The mass of water remains the same, but the volume increases.
6. Since Density=Mass/Volume, increasing volume decreases density.