Q1) A: I would say metals, because in reality transition metals are the largest category on the periodic table, and transition metals are closest to metals.
Q2) D: This is a trend in all columns of the periodic table.
Q3) D: Every element on the periodic table can form compounds, and the amount of elements on the periodic table are approximated down to be about 100.
Q4) B: Periods is the answer. Groups are columns (vertical).