–a) Solutions of lithium carbonate and ethanoic acid are mixed.

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–b) Solutions of sodium sulfide and sulfuric acid are mixed.

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–c) A spatula of potassium hydrogensulfite is dropped in hydrochloric acid in a beaker.

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–d) A spatula of sodium oxide is added to ethanoic acid in a beaker.

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–e) A small amount of magnesium sulfide is added to hydrochloric acid in a beaker.