The things or apparatus not used Joseph Priestly was:
(A) Sun rays
(B) Mercuric oxide
(C) Convex lens
(D) Bell jar

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Hint: Joseph Priestly was a British scientist who has been credited to the isolation and identification of various gases like sulphur dioxide, nitrogen dioxide and ammonia. But one of his most important discoveries is that of oxygen.

Complete Step-by-Step Solution:
While serving under the Earl of Shelburne in the year 1773, Joseph Priestly conducted several experiments. It was during this time that he stumbled upon a unique gas that truly stumbled him.
The setup of the entire experiment can be explained as follows:
Initially, he experimented using his “burning lens” (convex lens) to heat up a sample of mercuric oxide. He then observed that a remarkable gas was emitted from the burning of mercuric oxide. After that, Joseph Priestly conducted a series of experiments in 1773 to understand the importance of air for the survival of living organisms. The subjects for observation that he chose were a mint plant, a mouse, a burning candle. All these were placed in a bell jar as required.
Hence, from this we can conclude that the things or apparatus not used by Joseph Priestly was sun rays.

Hence, Option A is the correct option.

Note: This experiment paved the way for understanding and categorizing various such gases and Joseph Priestly although with an accidental beginning, discovered oxygen.