Question

Number of atoms in a formula CaCl2

Answer 1

One Calcium atom and two chlorine atoms

When looking at a formula like this the subscripts and coefficients ususally determine how many atoms are in the formula for example in H20 there are 2 Hydrogen atoms because after the H there is a 2; and there is only one Oxygen atom because their is not a subscript. and a subscript is comes usually after a atom in a formula and is smaller and below the elements while a coefficient would be before the elements in a formula and be a large number.

side note; you can only change the coefficients when balancing formulas the subscripts never change.