instruction:
Given a scientific question, generate a correct answer to it.
question:
What physical property of matter reflects how closely packed the particles are?
answer:
density

question:
Carboxylic acids have an acidic hydrogen atom, but esters do not. what do esters have in place of an acidic hydrogen atom?
answer:
hydrocarbon group

question:
How many valence electrons does a sodium atom have ?
answer:
one