Will the compound o2 be joined by an ionic or covalent bond

It's joined by a double covalent bond.

Both oxygen atoms want to gain 2 electrons to have a full outer shell of 8 he ce being the most energetically stable. so each atom shares 1 pair of electrons. this is a special type of covalent bond, called a dative covalent

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.