The chemical formula CH2O can be classified as Empirical formula and possibly a molecular formula. The empirical formula of a compound is the simplest formula that indicates the simplest ratio of atoms in the compound, while the molecular formula is the representation of the actual whole number ratio between the elements of the compound.
Elements Y and elements Z would have similar properties due to the fact that they both posses the same number of valence electrons. They both have a single valence electron that determines the corresponding elements bonding properties and the fact that it can either donate 1 valence electron to produce an ion that would be attracted to another atom, that is also an ion. Assuming that these elements are group 1 elements, they do not undergo in covalent bonding.