Which procedure would best allow a scientist to observe a chemical property of hydrochloric acid (HCI) solution?
cooling the HCI solution until it becomes solid, and measuring this temperature
adding zinc to the HCl solution and observing whether or not bubbles are produced
placing a conductivity probe into a beaker of HCl solution to determine if it conducts electricity
measuring the mass of and volume of a sample of HCl solution to find its density

Adding Zinc to the HCl solution and observing whether or not bubbles are produced.

Explanation:

To observe the chemical property of Hydrochloric acid, HCl, the scientists can  treat it with an metal, if it produces an hydrogen gas then it is an acid.

Here the scientists are adding Zinc (Zn) metal with the acid HCl, it produces bubbles of the hydrogen gas which clearly shows the chemical property of an acid and confirms that it is an acid.

Zn + 2 HCl → ZnCl₂ + H₂ ↑

So adding metal to the acid confirms its nature.

thats a little if u want the answer just look it up on google thats what i do haha : )