Please help Im not sure what is the answer.

The boiling point of propanoic acid is higher than that of 1-butanol because: propanoic acid has a higher molecular weight than 1-butanol. propanoic acid is more soluble in water than 1-butanol. propanoic acid is a better hydrogen bond donor than 1-butanol. propanoic acid forms hydrogen bonded dimers and 1-butanol does not. 1-butanol forms hydrogen bonded dimers and propanoic acid does not.

The number to the right of an element's symbol (ex. c-12) identifies the of an isotope.

Which of the following is true about the speed of light? it depends on the wavelength.