10. Summarize the effect of hydrogen bonding on boiling point. 11. Hydrogen fluoride (HF) has a lower boiling point than water, even though fluoride (F) has a greater electronegativity than oxygen (O). Why do you think that is?

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

a polar bond is formed when electrons are shared unevenly between atoms

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

the maximum mass of nh3 is nh3 in grams