What is an atom? A An atom is a round spherical object found inside most objects made of
matter
B. An atom is a round spherical object found inside objects made of matter
C. An atom is a basic building block of matter.
D. An atom is a subunit of longer extended structures.

C because I know it is

If a hydrogen atom is neutral, it must also have  one electron. an oxygen atom (o) has an atomic number of eight (8). this means a neutral oxygen atom has eight protons and eight electrons. the element actium (ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom