<P> Not all halogens react with the same intensity . Fluorine is the most reactive and combines with most elements from around the periodic table . As with other columns, reactivity decreases as the atomic number increases . </P> <P> When a halogen combines with another element, the resulting compound is called a halide . One of the best examples of a halide is sodium chloride (NaCl). </P> <P> The d - block is on the middle of the periodic table and includes elements from columns 3 through 12 . These elements are also known as the transition metals because they show a transitivity in their properties i.e. they show a trend in their properties in simple incomplete d orbitals . Transition basically means d orbital lies between s and p orbitals and shows a transition from properties of s to p . </P> <P> The d - block elements are all metals which exhibit two or more ways of forming chemical bonds . Because there is a relatively small difference in the energy of the different d - orbital electrons, the number of electrons participating in chemical bonding can vary . This results in the same element exhibiting two or more oxidation states, which determines the type and number of its nearest neighbors in chemical compounds . </P>

What groups of elements does the d-block contain