The number of metals among the following element are
`(24)/(12)X, (19)/(9)Y, and (31)/(15)` Z

Explanation

From the atomic numbers, the electronic configurations may be written. The electronic configurations can help us to predic whether the given element is a metal or not. (b) `(19)/(9)` Y : The atomic number is 9 and its electronic configuration is 2, 7. SInce it has more than 3 electrons in its valence shell, it is not a metal.
(c) `(31)/(15)` Z : The atomic number is 15 and its electronic configuration is 2, 8, 5. It is not a metal.