I need help with a chemistry problem? PLEASE?

[TeeL8758]

In what kind of reaction does one element replace a similar element in a compound?The energy released when a covalent bond forms is the difference between zero and theA)maxium potiential energyB)kinetic wnergy of the atomC) minimum potential energyd) bond length expressed in nanometersIn a chemical equation 2mg(S) + o2(g) ? 2MgO(s)A)mg rpresents the product magnesiumb) the reaction yeilds magnesiumc) mg represents the reagent magnesiumd) O2 rpresents the product oxygen gasAs atoms bond with each other what happens to them?

[JulieJ]

a, d