Which of these pairs of elements have the same number of valence electrons
phosphorus (p) and chlorine (cl)
beryllium (be) and calcium (ca)
chlorine (cl) and helium (he)
oxygen (o) and carbon (c)

Tin has ten stable isotopes. the heaviest, 124sn, makes up 5.80% of naturally occuring tin atoms. how many atoms of 124sn are present in 82.0 g of naturally occurring tin? what is the total mass of the 124sn atoms in this sample?

What are transitions between a liquid and gas called? identify which way they are transitioning

An experimental procedure requires a 10 ml of acid to be dissolved