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Q.
An element $X$ has atomic number $19$. What will be the formula of its oxide?
Classification of Elements and Periodicity in Properties
Solution:
Element $X$ has atomic number $19$. Its valency will be one. Hence, the formula of its oxide will be $X_2O$.
$ Z = 19$; $1s^2\, 2s^2\, 2p^6\, 3s^2\, 3p^6\, 4s^1$