Final answer:
If an atom or molecule doesn't have a subscript or coefficient, the number that should be used is 1. A lack of subscript in a chemical formula indicates only one atom of the element is present within the molecule. Subscripts represent the number of atoms of an element within a single molecule, while coefficients denote how many molecules of a substance there are.
Step-by-step explanation:
If an atom or molecule doesn't have a subscript or coefficient, the number that should be used for that atom or molecule is 1. When you see a chemical formula, like H2O for water, it indicates that there are two hydrogen atoms for every one oxygen atom. If only one atom is present and there is no subscript, as in the case of ammonia (NH3), it's understood that there is one nitrogen atom for the three hydrogen atoms. The correct answer to the question is B. 1.
Understanding the difference between subscripts and coefficients is essential in chemistry. A coefficient indicates the number of molecules of a substance, while a subscript denotes the number of atoms of an element within a single molecule. For example, '2H2O' indicates two separate molecules of water, each containing one oxygen and two hydrogen atoms, while 'H2' refers to a single diatomic hydrogen molecule.