Which of the following statements are true for pure substances?
(i) pure substances contain only one kind of particles
(ii) pure substances may be compounds or mixtures
(iii) pure substances have the same composition throughout
(iv) pure substances can be exemplified by all elements other than nickel.

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) State one characteristic property of gas D.
(e) Write one test to identify gas E.

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) Which 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.