Why is hydrogen a light gas, but iron is a heavy solid

Sorry for the plain answer but Hydrogen is a *Light* Gas and iron is Iron -- heavy

Good question, but...
I think this is how it is, hydrogen is a light gas, iron has many other elements, and that's what makes it heavy -

If a hydrogen atom is neutral, it must also have  one electron. an oxygen atom (o) has an atomic number of eight (8). this means a neutral oxygen atom has eight protons and eight electrons. the element actium (ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom

Sorry i dont understand the question can you rephase it?