To determine which atom could represent X in the molecule CaX, we need to consider the typical bonding characteristics of calcium (Ca) and the other elements listed.
Calcium is an alkaline earth metal located in Group 2 of the periodic table. It typically forms a +2 charge cation (Ca²⁺) because it tends to lose two electrons.
Let’s analyze the options:
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Bromine (Br): Bromine is a halogen in Group 17, which typically forms a -1 charge anion (Br⁻). Since Ca can lose two electrons and Br can gain one, two bromine atoms can bond with one calcium atom to form CaBr₂.
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Oxygen (O): Oxygen is in Group 16 and typically forms a -2 charge anion (O²⁻). One calcium ion (Ca²⁺) can bond with one oxide ion (O²⁻) to form a stable molecule CaO.
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Boron (B): Boron is in Group 13 and does not generally form a simple ionic bond with calcium to create an ionic compound like CaB.
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Carbon (C): Carbon is in Group 14 and typically forms covalent bonds, rather than ionic bonds, with metals like calcium. While it can form various compounds, it does not readily form a simple ionic compound with calcium in the form of CaC.
The best candidates that can form stable ionic compounds with calcium are bromine (Br) and oxygen (O). However, since the query is looking for a single atom that represents X, oxygen (O) is the most straightforward representation because it forms a direct 1:1 ionic bond with calcium.
Thus, the best answer for X in the compound CaX is:
oxygen (O)