Question

how many moles of mercury 2 oxide are needed to produce 125 grams of oxygen

Answer 1

2 HgO >> 2 Hg + O2
moles O2 = 125 g / 32 g/mol =3.91
the ratio between HgO and O2 is 2:1
moles HgO needed = 2 x 3.91 =7.82
Hope this helps!