Amolecule of an unsaturated hydrocarbon must have 1) at least one single carbon-carbon bond 2) at least one multiple carbon-carbon bond 3) two or more single carbon-carbon bonds 4) two or more multiple carbon-carbon bonds

2) at least one multiple carbon-carbon bond.

Explanation:

So, A molecule of an unsaturated hydrocarbon must have 2) at least one multiple carbon-carbon bond.

a  solution  is always transparent, light passes through with no scattering from solute particles which are molecule in size. the  solution  is homogeneous and does not settle out. a colloid is intermediate between asolution  and a  suspension. while asuspension  will separate out a colloid will not.