A. hydrochloric acid
B. mercury
C. calcium chloride
D. tetraoxosulphate (VI) acid

Correct Answer:

Option B – mercury

Explanation

Oxygen is usually collected over water because the solubility of the gas in water is not high. If the gas is needed dry, then it can be passed through a drying agent, like anhydrous calcium chloride or quick lime, or concentrated sulphuric acid, and then collected over mercury.

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