Here's how to figure out the percentage of chlorine in NaCl (sodium chloride):

1. Find the molar masses:

* Sodium (Na): 22.99 g/mol

* Chlorine (Cl): 35.45 g/mol

2. Calculate the molar mass of NaCl:

* 22.99 g/mol (Na) + 35.45 g/mol (Cl) = 58.44 g/mol

3. Determine the proportion of chlorine:

* (35.45 g/mol Cl) / (58.44 g/mol NaCl) = 0.6066

4. Convert to percentage:

* 0.6066 * 100% = 60.66%

Therefore, NaCl is approximately 60.66% chlorine by mass.