how many atoms are in CaCO3

Answer 1

In this compound there are 5 atoms.

the number of atoms in a compound is determined by adding up all the subscripts in the chemical formula

though if there is only 1 of a given atom you do not write the subscript for that atom

So while the chemical formula means Ca₁C₁O₃ you would write it as CaCO₃

and by adding the subscripts together you get a total of 5 atoms.

(subscripts are the small numbers written beside and slightly below the letters in the chemical formula)