Is the fact that table salt is composed of Na & Cl a chemical or physical property?
The problem rises when we are mistaken about what a property is. 


  The different types of matter can be distinguished through two components: composition and properties. UCDavis


Do a search about chemical property, and you get:


  a property or characteristic of a substance that is observed during a reaction in which the chemical composition or identity of the substance is changed. Dictionary.com
  
  A chemical property is any of a materials properties that becomes evident during a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity. Simply speaking, chemical properties cannot be determined just by viewing or touching the substance; the substance's internal structure must be affected for its chemical properties to be investigated. However a catalytic property would also be a chemical property. Wikipedia
  
  Any characteristic that can be determined only by changing a substance's molecular structure.
   Boundless


What's a physical property?


  A physical property is any property that is measurable whose value describes a state of a physical system. The changes in the physical properties of a system can be used to describe its transformations or evolutions between its momentary states. Physical properties are often referred to as observables. They are not modal properties. - Physical property in wikipedia.


Basically, a physical property is what that doesn't deal with the composition of matter; but other factors, such as it's physical state. "Physical" isn't at its literal meaning.

Table salt is never pure $\ce{NaCl}$; because simply there's nothing pure in the nature. It's mainly composed of Sodium Chloride crystals. But if, and only if, we consider it to be only made from $\ce{NaCl}$, we are talking about its chemical composition and therefore, it must be a chemical property.

I understand that sometimes there are wrong questions for us to answer, so if composition is to be a property, it must be a chemical one.