Question

can someone help, please ??
Chemistry

1. The periodic table is based on an element's
A. molecular size.
B. molecular mass.
C. atomic mass.
D. atomic number.

2. One atom of silicon can properly be combined in a compound with
A. two atoms of oxygen.
B. one atom of chlorine.
C. three atoms of hydrogen.
D. four atoms of calcium.

Answer 1

I know number one is D for sure but number two doesn't explain enough or perhaps I don't quite understand it