A student takes four samples of a silver, metallic solid and and subjects each piece to different treatment. Piece 1: The solid is hammered into a flat sheet. Piece 2: The solid is heated in a flame until it melts. Piece 3: The solid fizzes when acid is dropped on the surface. Piece 4: The solid is place in a beaker of water and it floats.

Explanation:

A chemical change  is only manifested when a chemical reaction occurs, which means that the original substance is transformed into one or more different substances. In a chemical change either the original substance decomposes (by action of the heat, light or other influence) or combines with other substances, becoming a new substance.

Piece 1: The solid is hammered into a flat sheet.

In this case the silver has not been transformed into a different substance; it has only changed its shape. Thus, this is just a physical change.

Piece 2: The solid is heated in a flame until it melts.

Again, the final substance is still silver. It has only suffered a change of state. Thus, this is a physical change too.

Piece 3: The solid fizzes when acid is dropped on the surface.

Fizzing is a sign that a new substance has formed. In this case, the acid reacted with the piece of silver, forming a compound of silver and a gas (likey hydrogen).

Typically metals react with acids forming a salt ans hydrogen gas.

Piece 4: The solid is place in a beaker of water and it floats.

The silver has not suffered any change.