There are three substances X, Y and Z. The substance X does not have a fixed melting point or boiling point and it still shows the individual properties of its constituents. The substance Y is a pure substance which occurs in nature as such. The substance Y has a fixed melting point and boiling point but it cannot be broken down into simpler substances by any chemical means. The substance Z is also a pure substance whose properties are entirely different from those of its constituents. The substance Z can, however, be divided by electrolysis into two substances which belong to the same class of substances as Y.

(a) What type of substance could X be? Name one substance like X.

(b) What type of substance could Y be? Name one substance like Y.

(c) What type of substance could Z be? Name one substance like Z.

(d) Whish process involves absorption or release of an appreciable amount of energy: formation of substance X or formation of substance Z?

(e) Name the three groups into which all the substances like Y are divided on the basis of their properties.

In the following set of substances, one item does not belong to the set. Select this item and explain why it does not belong to the set:

Hydrogen, Oxygen, Steam, Chlorine

Iron powder and sulphur powder were mixed together and divided into two parts A and B. When part A was heated strongly over a burner, then a substance C was formed. The part B was, however, not heated at all. When dilute hydrochloric acid was added to substance C, then gas D was evolved and when dilute hydrochloric acid was added to part B then gas E was evolved.

(a) What type of substance is B?

(b) What type of substance is C?

(c) Name the gas (i) D, and (ii) E?

(d) Write one characteristic property of gas D.

There is a large group of materials P which can be divided into three groups Q, R, and S on the basis of their properties. The substances belonging to group Q can be solids, liquids or gases. The solids belonging to group Q are usually electrical insulators. Most of the substances of group R are solids which are good conductors of electricity. The substances belonging to group S are neither insulators like Q nor good conductors like R. The properties of S are intermediate between those of Q and R.

(a) What could the group of materials P be?

(b) Name the substances Q. Give two examples of such substances.

(c) Name the substances R. Write two examples of such substances.

(d) Name the substances S. Give two examples of such substances.

(e) Out of Q, R and S, which substances are malleable and ductile?

A, B and C are all liquids. Liquid A has a comparatively low boiling point. On heating, liquid a vaporizes completely without leaving behind any residue. Liquid A is being used increasingly as a fuel in motor vehicles either alone or by mixing with petrol. Liquid B has a very high boiling point. It also vaporizes completely on heating, without leaving any residue. Liquid B is a conductor of electricity and used in making thermometers. Liquid c has a moderate boiling point. On heating, liquid C vaporises leaving behind a white solid D which is used in cooking vegetables. The condensation of vapours from C give a liquid E which turns anhydrous CuSO₄ to blue.

(a) Which liquid could be an element? Name this element.

(b) Which liquid could be a mixture? Name this mixture.

(c) Which liquid could be a compound? Name this compound.

(d) What could the solid D be?

(e) What do you think is liquid E?