An element X has a valency of H. Write its formula for carbonate?

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answer is C.

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Detailed Solution

Concept- Valency is the number of electrons an atom required to achieve a stable octet configuration. If the last shell contains more than 4 electrons, it accepts electrons otherwise it loses electrons for stability.
Now, Element X has the same valency as that of H. The valency of H is 1. So, the valency of element X is also 1.
The formula of the carbonate ion is

C O_{3}^{2 -}

and thus the charge on the carbonate ion is -2.
The crisscross method is used to write the formula of an ionic compound. As per the crisscross method, the numerical value of each of the ionic charges crosses over to become the subscript of the other ion.
Therefore, the carbonate formed with element X is

.
Hence, the correct answer is 3.

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