Hey i have a chemistry problem pls tell me how do you find the percentage

What is the smallest component or the most basic building block of any element ? a. an atom, b.a compound c.gas d.element

What effect would average population growth have on land usage? a. urban use of land would rise to more than 30 percent of available land. b. industrial use of land would rise to more than 30 percent of available land. c. the percentage of available land used as cropland would stay the same. d. cropland would fall to about 10 percent of available land.

The kw for water at 0 °c is 0.12× 10–14 m2. calculate the ph of a neutral aqueous solution at 0 °c.