What is the number after an elements name, representing the sum of its protons and neutrons

How many moles of air are there in a human lung with a volume of 2.4 l at stp? explain your answer

Word equation for k(s) +h2o(l) yield koh (aq) + h2

What are the advantages of using the metric system? designed as a decimal system making conversions simpler more accurate system of measurement has prefixes that correspond to an amount to use with all base units used by the entire scientific community