Table salt is 40% sodium by mass. What is true about all sodium chloride? A. The mass of sodium is sometimes 30% by mass.
B. Not all sodium chloride will contain 40% sodium by mass.
C. All sodium chloride will contain 40% sodium by mass.
D. The ratio of sodium to chlorine in sodium chloride will vary.

C. All sodium chloride will contain 40% sodium by mass.

Explanation:

It is definitely true that all sodium chloride will contain 40% sodium by mass. Table salt is the common name of sodium chloride which is the chemical name.

The formula is designated as NaCl.

According to the Law of constant composition or definite proportions; "all pure samples of the same compound contain the same proportions of the elements by mass".

This implies that every time a particular compound forms, it forms in the same percentage composition. It forms in the same percentage composition.

So, we see that all sodium chloride will contain 40% sodium by mass.

Option A, B and D are in contradiction with the law of constant composition.