Class 9 Science Chapter 2 MCQ

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

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].

Milk is considered to be an impure substance as it is an emulsion. Emulsion is a colloid in which minute droplets of one liquid are dispersed in another liquid, which is not miscible with it.

Actually, rusting of an article, made up of iron is called corrosion. Corrosion is a chemical change because rust is a chemical compound (hydrated iron oxide) which is totally different from element iron (Fe). Physical changes are those changes in which no new substances are formed. The substances do not change their identity and they can be easily returned to their original form by some physical processes. Example – melting of ice, glowing of an electric bulb, breaking of glass tumbler etc. On the other hand, chemical changes are those changes in which new substances are formed. The substances involved change their identity and they get converted into entirely new substances, which cannot be returned to their original form i.e. burning of paper, rusting of iron, burning of magnesium wire etc. Note: Dissolution is the process in which a solute is dissolved in a solvent to form solution.

In a true solution (like sugar solution), the solid particles are so small that they cannot scatter light rays falling on them. For example, if a beam of light (from a torch) is put on true solution (like sugar solution) kept in a beaker in a dark room, the path of light beam is invisible inside the solution when seen from the side. The beam of light can become visible only when the solid particles are big enough to reflect light falling on them. Since the particles of a true solution do not a scatter light.

The chemical changes are permanent changes which are usually irreversible.

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

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.

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