How many atoms are there in 1 mole of H2O, and how would you calculate this?

A mole refers to ##6.022 x 10^23## items. ##H_2O## has 2 hydrogen atoms and 1 oxygen atom...so a total of 3 atoms in each ##H_2O##.

Therefore ##(6.022 x 10^23)x ## (3 atoms) ##=18.066 x 10^23##

Then we need to change the answer into proper : ##18.066 x 10^23 = 1.8066 x 10^24##

Lastly, change to proper number of . There are 4 significant figures in 6.022. Due to this we need to also have 4 significant figures in the final answer, so we would round ##1.8066 x 10^24 to 1.807 x 10^24##

So, your final answer is: ##1.807 x 10^24##