2 Answers

there are 2 Hg per molecule of that Hg2(NO3)2
there are 2 N per molecule of Hg2(NO3)2
there are 6 (3×2) O per molecule of Hg2(NO3)2
So for 1 mole Hg2(NO3)2 you get 2 mol Hg, 2 mol N, and 6 mol O

2 Hg
2 N
6 O
there are 2 Hg per molecule of that Hg2(NO3)2
there are 2 N per molecule of Hg2(NO3)2
there are 6 (3×2) O per molecule of Hg2(NO3)2
So for 1 mole Hg2(NO3)2 you get 2 mol Hg, 2 mol N, and 6 mol O
2 Hg
2 N
6 O