Science M.C.Q. [1 M]

Ice and air are homogeneous in nature as their compositions remain same throughout.

Copper is a good conductor of electricity. It means that it offers very low electric resistance. Also, it is highly ductile due to which it can be drawn into very thin wires.

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.

Metals are malleable and ductile as they can be hammered into thin sheets and can be stretched into wires.

Sugar solution does not show Tyndall effect because sugar solution is a true solution and not a colloid.

Silica does not sublime on heating.

When a mixture of iron and sulphur is heated strongly, they first absorb the energy to get excited. This is followed by the formation of a new compound iron sulphide (FeS) with the release of huge amount of energy in the form of heat and light.

Chalk in water will most likely scatter the beam of light when passed through it because it forms a suspension.

Milk and groundnut oil are two immiscible liquids. So, they can be separated by using a separating funnel.

Mixture of sand and sulphur cannot be separated by using water as a solvent because both are insoluble in water.

Germanium is metalloid. It is neither a good conductor of electricity nor an insulator. It is a semiconductor.

Naphthalene sublimes on heating, whereas sand does not. So, when the mixture is heated, solid naphthalene turns into vapours, which can be condensed. Sand remains in the container.

Mercury is a metal that exists in liquid state and bromine is a non-metal that exists in liquid state.

Milk of magnesia is a suspension of magnesium hydroxide in water. It has milk like texture.

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

Chromium does not have magnetic property. Therefore, it will not be attracted by a magnet.

Centrifugation is a process, in which suspended particles are separated from the solvent. In this process, the solution is rotated at a high rate in a centrifuge thereby separating the solute particles and the solvent.

Crystallisation is a better technique to recover sugar from sugar solution because sugar decomposes or gets charred on heating. Also, the soluble impurities get removed by crystallisation.

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.

Brass is an example of solution of solid in solid. It is an alloy of copper and zinc.

Brine is salt solution. When it is heated, water will evaporate and salt will be left as residue.

Hydrogen cannot be separated from the mixture of air as it is not present in free state. The three major components of air are nitrogen, oxygen and argon. These are separated using fractional distillation.

Boron, silicon and germanium are metalloids. Gallium is a metal.

Air is a homogeneous mixture of different gases. Hence, it does not have a fixed melting or boiling point.

Chromatography is the technique used to separate the contents of a mixture, where solute particles are in extremely small quantity.

Milk of magnesia is a suspension of magnesium hydroxide in water. It has a milk-like texture. The particles are suspended in the solvent. Milk is a colloid, whereas salt solution and vinegar are solutions.

Shaving cream is not an emulsion but foam.

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

In the mixture of iodine and alcohol, both are miscible. So, distillation process is used to recover both the components.

Air, kerosene oil and petrol are mixtures of various compounds of carbon and hydrogen (called hydrocarbons). Alcohol is a compound and not a mixture.

Sulphur is soluble in carbon disulphide but carbon is not.

Crystallization is the process of cooling a hot concentrated solution of a substance to obtain its crystals in pure form.

Iodine dissolved in alcohol is called tincture of iodine.

Sulphur dissolves completely in carbon disulphide. So, it forms a homogeneous solution. As the particles of solute are too small to scatter light, they will not cause tyndall effect.

Chlorine is added to water to purify it from the impurities such as bacteria.

Sublimation of naphthalene is not a chemical change because it only allows naphthalene to change its state from solid to vapour. No new compound is formed and the vapour can again be condensed to solid form.