There are times when you should request copies of your records: 1  Permanent Change of Station. 2  Deploying. 3  Retiring.
0. EXPERT ANSWER. Double coincidence of wants refers to a situation in a barter system where the goods or services offered by a seller are exactly the same as that required by a buyer and vice versa.
A double covalent bond is where two pairs of electrons are shared between the atoms rather than just one pair. Two oxygen atoms can both achieve stable structures by sharing two pairs of electrons as in the diagram. The double bond is shown conventionally by two lines joining the atoms.