How is the propulsion necessary to move a spacecraft through space different from the propulsion necessary to move an
airplane through the air?

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

answer: i have one answer

acids are substances that ionize (break off) in an aqueous solution to produce hydrogen (h+) ions

explanation:

hope this and sorry i could only come up with one answer!