Given: 2NaCl the 2 is:

A. a coefficient that represents the number of sodium atoms in the molecule.
B. A subscript that represents the number of sodium atoms in the molecule.
C. A coefficient that represents the number of sodium chloride molecules.
D. A subscript that represents the number of sodium chloride molecules.

The answer to your question is the letter C.

Explanation:

Data

        2NaCl

When we write molecules we use numbers in two main different ways.

If the coefficients are at the beginning of the molecule, this number indicates the number of molecules presented.

If there are subscripts, this number indicates the quantity of that specific element.

So the correct answer is letter C because it describe the correct function of this coefficient.

n+h→nh3

we must remember that nitrogen and hydrogen are both diatomic molecules in their standard gas form. this adjusts the equation to

n2+h2→nh3

now we need to adjust coefficients in order to balance the atoms on each side of the equation. currently we have 2 atoms of nitrogen and 2 atoms of hydrogen on the reactant side and 1 atom of nitrogen and 3 atoms of hydrogen on the product side.

we can balance the hydrogens by placing a coefficient of 2 in front of ammonia and a coefficient of 3 in front of the hydrogen.

n2+3h2→2nh3

this gives us 6 hydrogen on each side and coincidentally the nitrogens now equal 2 on each side.

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