Sure, let's analyze each of the given compounds to determine which one contains an ionic bond.
1. Option A: [tex]\( O_2 \)[/tex]
- This is a molecule composed of two oxygen atoms.
- Both atoms are identical non-metals and they share electrons equally, forming a covalent bond.
- Therefore, [tex]\( O_2 \)[/tex] does not contain an ionic bond.
2. Option B: [tex]\( CaO \)[/tex]
- This is a compound formed by calcium (Ca) and oxygen (O).
- Calcium is a metal, and oxygen is a non-metal.
- Metals tend to lose electrons and become positively charged ions (cations), while non-metals tend to gain electrons and become negatively charged ions (anions).
- In [tex]\( CaO \)[/tex], calcium loses two electrons to become [tex]\( Ca^{2+} \)[/tex] and oxygen gains those two electrons to become [tex]\( O^{2-} \)[/tex].
- The electrostatic attraction between [tex]\( Ca^{2+} \)[/tex] and [tex]\( O^{2-} \)[/tex] forms an ionic bond.
- Therefore, [tex]\( CaO \)[/tex] contains an ionic bond.
3. Option C: [tex]\( H_2O \)[/tex]
- This is a molecule formed by two hydrogen atoms and one oxygen atom.
- Both hydrogen and oxygen are non-metals.
- They share electrons to form covalent bonds (specifically polar covalent bonds due to the difference in electronegativity).
- Therefore, [tex]\( H_2O \)[/tex] does not contain an ionic bond.
4. Option D: [tex]\( CH_4 \)[/tex]
- This is a molecule composed of one carbon atom and four hydrogen atoms.
- Carbon and hydrogen are both non-metals.
- They share electrons to form covalent bonds.
- Therefore, [tex]\( CH_4 \)[/tex] does not contain an ionic bond.
After examining all the options, we can conclude that the compound containing an ionic bond is:
Option B: [tex]\( CaO \)[/tex]
