Which of the following is the correct use of sodium nitrate $\left(\mathrm{NaNO}_3\right)$?
A) It is used in the preparation of fertilizers.
B) It is used in food preservation.
C) It is used in the production of explosives.
D) All of the above.
Sodium nitrate is widely used in the production of fertilizers, food preservation (especially in curing meats), and as an oxidizer in the manufacture of explosives such as gunpowder. Therefore, all the options are correct.
Hence , the correct answer is option (4)
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