Answer:
Ionic bonding
Explanation:
Since Ca is a metal and O is a nonmetal, they will experience ionic bonding. This means that Ca will "donate" two of its valence electrons to O. This will give both Ca and O a complete octet.
Answer:
CaO
Explanation:
Depending on the element "a" stands for, there is not enough info to conclude how these elements would bond. however, if they are typed out correctly then one possible bond would be CaO. I am assuming that the C and O represent Carbon and Oxygen.