Olympiad Test: Is Matter Around us Pure- 2 - Class 9 MCQ

You can separate the sublimating substance (Naphthalene / Anthracene / Camphor / Ammonium chloride) from the mixture through the process of sublimation.

The rusting of iron is a chemical change because it is two substances reacting together to make a new substance. When iron rusts, iron molecules react with oxygen molecules to make a compound called iron oxide.

Magnetic separation works only on ferromagnetic materials (those strongly attracted to magnets).

• Cobalt, Steel, and Nickel → All are ferromagnetic, so they can be separated using magnetic separation.
• Chromium → Not ferromagnetic (it is antiferromagnetic in bulk and paramagnetic at room temperature), so it cannot be separated by magnetic separation.

To find the percentage concentration of alcohol in the solution, first calculate the total volume of the solution:
Total volume = 50 mL (alcohol) + 150 mL (water) = 200 mL.
Next, use the formula:
Concentration (%) = (Volume of solute / Total volume of solution) × 100
Substitute the values:
Concentration (%) = (50 / 200) × 100 = 0.25 × 100 = 25%
Therefore, the percentage concentration of alcohol in the solution is 25%.

Previously we told that, D∝ 1/√M

​Now, M_CO2 =2×16+12=44 g/mol

M_N2O=2×14+16=44 g/mol

∴D_CO2 =D_N2O , as diffusion coefficient of CO₂ and N₂O is equal, CO₂ and N₂O cannot be separated by diffusion method.

Decaying of wood and burning of wood, because there will be a change of chemical composition and wood cannot be restored to its original form. Sawing of wood and hammering of nails into a piece of wood are physical processes where the chemical composition of compounds is not changed.

Solid foam is a colloid in which a gas is dispersed in a solid medium, hence, Bread is an example of solid foam.

Mass by mass percentage of a solution = [(Mass of solute) / (Mass of solution)] X 100

Here, mass of solute ( cuSo₄) = 110g

Mass of solution = 550 g

Therefore mass by mass percentage of solution = (110 X 100) / 550= 20%

Hence, the concentration of the solution is 20%.

Ice and air are homogeneous in nature as their particles are not distinctly visible. A homogeneous mixture has a uniform composition throughout its mass. It has no visible boundaries of separation between its various constituents, e.g., air, sugar solution, brass, etc.

A heterogeneous mixture does not have a uniform composition throughout its mass.It has visible boundaries of separation between its various constituents, e.g., soil, wood, blood etc.

• Milk is a true emulsion. It consists of fat droplets suspended in water, making it a stable mixture.
• In an emulsion, one liquid is dispersed in another, which is usually not soluble in the first.
• Butter → This is actually a gel (liquid fat dispersed in solid water phase after churning), not a true emulsion.
• Whipped cream → foam (gas dispersed in liquid).
• Jelly → gel (liquid dispersed in solid).