Class 9 Science Chapter 2 MCQ

A2B is a compound made up of two elements A and B in a fixed ratio. The properties of a compound (e.g. A2B) are entirely different from those of its constituent elements (e.g. A and B). The composition of a compound is fixed.

Here, all these statements are correct. Hence your answer will be option [D].

Melting of iron metal, bending of an iron rod and drawing a wire of iron metal are physical changes, because in three processes, iron changes its form, not the chemical composition. In rusting of iron, its chemical composition is changed.

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. Example – 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. Example – soil, wood, blood etc.

A pure substance is made up of only one kind of particles like elements. The composition of pure compounds is also same throughout.

The substance which is dissolved in a liquid to make a solution is called solute and the liquid in which solute is dissolved is known as solvent. For example, salt solution is made by dissolving salt in water, so in salt solution “salt” is the solute and water is the “solvent”.

The use of process of evaporation for separating a mixture is based on the fact that liquids vaporize easily whereas solid do not vaporize easily. The changing of a liquid into vapors or gas is called evaporation. Evaporation is used to separate a solid substance that has dissolved in water or any other liquid. The dissolved substances is left as a solid residue when all the water or liquid has evaporated.

Here, are all the statements are correct. Hence, your answer will be option [D].

Crystallization is a better technique than evaporation of dryness because some solids decompose or get charred on heating to dryness during evaporation. There is no such problem in crystallization. The soluble impurities do not get removed in the process of evaporation, but such impurities get removed in crystallization.

The process in option [B] is a chemical change because rusting causes formation of a new compound. Other statements are examples of physical changes where no new compounds are formed. In the process mentioned in other statements, original form of iron can be obtained back from moulded forms.