Final answer:
The incorrect statement is D: 'Atomic size increases going down any group and also across any period,' because atomic size decreases across a period but increases down a group.
Step-by-step explanation:
The incorrect statement about the periodic table is option D: Atomic size increases going down any group and also across any period. This statement is not accurate because atomic size actually decreases across a period. As we move from left to right across a period, the number of protons in the nucleus increases, which increases the nuclear charge and pulls the electrons closer. However, atomic size does increase as we go down a group. This is because with each additional shell of electrons, the outermost electrons are further from the nucleus, resulting in a larger atomic radius.
Regarding the other options, densities and melting points generally do not increase across all groups (Option A), and reactivity trends differ between metals and non-metals. Reactivity of non-metallic substances generally decreases going down a group due to increasing size and shielding, which makes it harder for the atom to attract additional electrons (Option B). With groups of metals, reactivity typically increases going down a group because metallic character and the tendency to lose electrons increase (Option C).