Write chemical equations for reactions taking place when
i. Zinc carbonate is calcined.
ii. Ammonia gas is passed over heated copper (II) oxide.

25 Give reasons for the following
i. Silicon counts among metalloids
ii. Carbon is not used for making aluminium from aluminium oxide.
iii. For making hydrogen by reaction with hydrochloric acid, granulated zinc is preferred to a block of zinc. 26 Explain
i) Why sugar chars (turns black) when conc. H₂SO₄ is added to it?
ii) What is the blue colour of crystalline copper sulphate due to? 28 (i) What is the colour of potassium dichromate solution?
(ii) What is the colour of Cr³⁺ ion?
(iii) What property of SO₂ is responsible for bringing change of colour of potassium dichromate? 29 How is chloride of lime chemically different from calcium chloride? Why does chloride of lime gradually lose its chlorine when kept exposed to air?