* Pure elements are substances made up of only one type of atom.

Let's break down the list:

* MgCl2 (Magnesium Chloride): This is a compound made of magnesium (Mg) and chlorine (Cl) atoms.

* NaCl (Sodium Chloride): This is a compound made of sodium (Na) and chlorine (Cl) atoms.

* C3H8 (Propane): This is a compound made of carbon (C) and hydrogen (H) atoms.

* Ag (Silver): This is a pure element.

* Al (Aluminum): This is a pure element.

Therefore, the pure elements in the list are Ag (Silver) and Al (Aluminum).