In which group do all the elements have a valency of one?
(a) hydrogen, oxygen, chlorine
(b) potassium, hydrogen, sulphur
(c) sodium, chlorine, hydrogen
(d) sodium, hydrogen, sulphur

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Solution

(c) sodium, chlorine, hydrogen

Hydrogen can donate or share only one electron. Thus, its valency is one.
When one atom of hydrogen combines with one atom of chlorine, it forms hydrogen chloride, HCl. Therefore, valency of chlorine is also one.
Similarly, when one atom of sodium combines with one atom of chlorine, it forms sodium chloride, NaCl. Therefore, valency of sodium is also one.

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Question 15
Give the formulae of the compounds formed from the following sets of elements

(a) Calcium and fluorine
(b) Hydrogen and sulphur
(c) Nitrogen and hydrogen
(d) Carbon and chlorine
(e) Sodium and oxygen
(f) Carbon and oxygen

Write the balanced chemical equations of the following reactions.

(a) Sodium hydroxide + sulphuric acid $\to$ sodium sulphate + water

(b) Potassium bicarbonate + sulphuric acid $\to$ potassium sulphate + carbon dioxide + water

(d) Chlorine + sulphur dioxide + water $\to$ sulphuric acid + hydrogen chloride

(e) Silver nitrate $\to$ silver + nitrogen dioxide + oxygen

(f) Copper + nitric acid $\to$ copper nitrate + nitric oxide + water

(g) Ammonia + oxygen $\to$ nitric oxide + water

(h) Barium chloride + sulphuric acid $\to$ barium sulphate + hydrochloric acid

(i) Zinc sulphide + oxygen $\to$ zinc oxide + sulphur dioxide

(j) Aluminium carbide + water $\to$ aluminium hydroxide + methane

(k) Iron pyrites ( $F e S_{2}$ ) + oxygen $\to$ ferric oxide + sulphur dioxide

(l) Potassium permanganate + hydrochloric acid $\to$ potassium chloride + manganese chloride + chlorine + water

(m) Aluminium sulphate + sodium hydroxide $\to$ sodium sulphate + sodium meta aluminate + water.

(n) Aluminium + sodium hydroxide + water $\to$ sodium meta aluminate + hydrogen

(o) Potassium dichromate + sulphuric acid $\to$ potassium chloride + chromium chloride + water + chlorine.

(p) Sulphur + nitric acid $\to$ sulphuric acid + nitrogen dioxide + water.

(q) Sodium chloride + manganese dioxide + sulphuric acid $\to$ sodium hydrogen sulphate + manganese sulphate + water + chlorine.

Two gases found dissolved in natural water are

(a) oxygen and carbon dioxide

(b) hydrogen and oxygen

(d) chlorine and ammonia

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