1. which of the following are pure substances?
solutions
compounds
homogeneous mixtures
colloids

2. if an unknown substance can not be broken down into simpler substances, it is
a compound.
an element.
made of one kind of atom.
both an element and made of one kind of atom.

3. when a physical change in a sample occurs, which of the following does not change?
shape
temperature
volume

1) compounds

For example H2O, CO2, KNO3, H2SO4, CH4 are all compounds. All the molecules have the same composition. The composition of a molecule of H2O is the same of all molecules of H2O.

It is not the same for solutions, mixtures or colloids.

2) both an element and made of one kind of atom.

Compounds can be broken into the elements that constitue them.

3) When a physical change in a sample occurs, a change in shape, temperature or volume can happen.

Examples:

Shape change: fold a paper
Temperature change: evaporation of water absorbs heat from the surroundings.
Volumen change: boiling liquid causes the volume to increase.

You'd likely miss one choice. Compoistion does not change when physical change occurs.

The answer to that would be magnesium