How many hydrogen atoms are in 4 molecules of isopropyl alcohol, c3h7o?

There are 28 H atoms in four molecules of C₃H₇O.

No of H atoms = 4 molecules C₃H₇O × (7 H atoms/1 molecule C₃H₇O)

= 28 H atoms

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface.