Calcium-49, a radioactive isotope, has a half-life of 9 minutes. If an 80-gram sample of the isotope decays for 27 minutes, how many grams of the original sample remain? Select one:
a. 60
b. 10
c. 40
d. 20

When determining the shape of a molecule, it is important to draw a lewis dot structure first in order to see the total number a. electrons within the moleculeb. bonding and unshared pairs around central atomc. unshared pair within the molecule( i really need it )

What do electromagnetic waves carry? how are they produced through which media can they move? where do they transfer energy? what do they not transfer? what do mechanical waves carry? how are they produced? through which media can they move? where do they transfer energy? what do they not transfer?

Compare sympathetic and parasympathetic