Asubstance is composed of only one kind of atom cannot be separated into simpler substances are converted into another substance by chemical processes which category would you classify the substance

Hello.

A substance that is composed of only one kind of atom, and in which cannot be separated into simpler substances are converted into another substance by chemical processes are elements. Some examples are hydrogen, oxygen, iodine, radium, magnesium, etc.

calculate how many grams of ammonia can be produced from 4.21 grams of

n2 + 3h2 = 2nh3

my answer:

25.0g n2 x (1 mol/ 28.0gn2) x (2 mol nh3/ 1 mol n2) x (17.0g nh3/ 1 molnh3) = 30.36g n2

25.0g h2 x (1 mol h2/ 2.00g h2) x (2 mol nh3/ 3 mol h2) x (17.0g nh3/ 1 mol nh3) = 141.67g h2

lr = n2