A student converted 400 centimeters into meters. Which of the following shows the student's answer with the correct number of significant digits?

1.) which of the following is a molecule but not a compound? a. he b. f2 c. h2o d. ch4 2.) what is a physical combination of substances? a. a compound b. a molecule c. a mixture d. an element 3.) what is a chemical combination of substances? a. a compound b. an atom c. a mixture d. an element 4.) what is the relationship between the solute and solvent in a solution? a. they form a compound b. they form a mixture c. they form molecules d. they form chemical bonds 5.) the gases in air dissolve in water. what would be one way to reduce the amount of a gas dissolved in water? a. add more water b. reduce the air pressure c. increase the air pressure d. stir the water 6.) how would you determine the solubility of a substance? a. find how well it dissolved various substances. b. find the mass and the volume of the substance. c. find the temperature at which the substance evaporated. d. find how much i was able to dissolve in a solute. 7.) the periodic table organizes all of the kinds of a. molecules. b. compounds. c. atoms. d. ions. 8.)what distinguishes two substances combined to become a compound vs. two substances combined to become a mixture? a. whether they can be easily separated b. whether they chemically bond together c. whether they both are visible d. whether they are heterogeneous 9.) the principle components of air are: n2 78% o2 21% ar 0.95% co2 0.038% this is a solution of a. molecules and atoms. b. molecules. c. compounds and molecules. d. atoms.