What is the isotope notation for an element with a mass number of 49, and 21 protons? what is the atomic number and number of neutrons, as well?

How many liters of oxygen gas, at standard temperature and pressure, will react with 35.8 grams of iron metal? 4 fe (s) + 3 o₂ (g) → 2 fe₂o₃ (s)

Observation and experimentation have led many scientists to accept a theory about the origin of the universe. this theory is called the big bang theory. scientific evidence collected and observed by scientists around the world suggests that the universe is ever expanding from a hot and dense initial state. what makes this a scientific theory? (2 points)

To calculate percent by mass, use the equation below: calculate the percent by mass of each element. %n = % %h = % %o = %