In Part 4, students flame tested the gas produced in the reaction. What happened when a flame was held in the inverted the test tube above the metal reacting with hydrochloric acid

A "squeaky" pop sound is heard.

Explanation:

When a metal reacts with hydrochloric acid, it produces the metal chloride (salt) and further liberates hydrogen gas which is a colourless and odourless gas.

Equation of the reaction

M (s) + HCl (aq) - -> MgCl (aq) + H2 (g)

A burning splint test is carried out for the identification of gases in the laboratory. A characteristic property of Hydrogen gas is that it gives a distinctive 'squeaky pop' sound.

Hydrogen is easily ignited, as it is flammable over a wide range of concentrations in air.