Determining the identity of substances is a critical part of chemistry because once the substance's identity is known, we can predict its behavior and understand the scenarios that it is involved in better.
For example, consider an industrial pipe where fouling (scaling) is occurring. If the compounds present in the scales are identified, steps may be taken to prevent and remove the scaling. This is one of many examples where identifying chemical substances is of high importance.
Answer:
c. Cr
Explanation:
The compound is containing 
ion.
If acid reacts with it, CO_2 evolves.
therefore, Cr would form a precipitate when added to an aqueous solution of this compound. Cr2CO3 is the precipitate.
Answer:
The symbol for an atom indicates the element via its usual two letter symbol, the mass number as a left superscript, the atomic number as a left subscript (sometimes omitted), and the charge as a right superscript.
Explanation:
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