Brine is a concentrated aqueous solution of sodium chloride.

Here are the solutions to questions 14-20:

14. Brine is a concentrated aqueous solution of sodium chloride.

    • The correct option is D.

15. Concentrated nitric acid passivates iron by forming a protective, insoluble layer of iron(III) oxide ($Fe_2O_3$) on its surface, which prevents further reaction.

    • The correct option is A.

16. Copper is less reactive than hydrogen in the reactivity series. Therefore, it does not react with dilute acids like hydrochloric acid to liberate hydrogen.

    • The correct option is B.

17. In cuprous salts, copper has an oxidation state (valency) of +1. In cupric salts, copper has an oxidation state (valency) of +2.

    • The correct option is A.

18. When pure copper is exposed to rain and air, it forms a green layer known as patina. This layer is primarily composed of basic copper(II) carbonate, $Cu_2(OH)_2CO_3$.

    • The correct option is A.

19. Hard water contains dissolved mineral ions, primarily calcium ($Ca^{2+}$) and magnesium ($Mg^{2+}$) ions.

    • The correct option is C.

20. Let's evaluate each statement:

    • (i) Hard water often contains dissolved minerals that can improve the taste of water for many people. This is an advantage.
    • (ii) Hard water reacts with soap to form scum, which means it wastes soap. This is a disadvantage.
    • (iii) Hard water contains calcium and magnesium ions, which are essential for strong bones and teeth. While the phrasing "used by NaCl" is incorrect, the underlying benefit of Ca/Mg in hard water for health is an advantage.
    • (iv) The mineral content of hard water can be beneficial for certain processes, such as brewing, influencing the flavor and fermentation. This is an advantage.

    Considering the advantages (i), (iii), and (iv), and the given options, option B includes two commonly recognized advantages.

    • The correct option is B.