60 point! please help me please!

Explanation:

Here,

for 1 mol of O₂, 2 moles of MgO are produced.

Also,

At STP:

1 mol of O₂ = 22.4 dm³/mol molar value

Moles in 242 L of O₂:

= volume / molar value

= 242 / 22.4

= 10.8 mol

Since:

1 mol of O₂ = 2 moles of MgO

10.8 mol of O₂ = 2 × 10.8 moles of Mgo

10.8 moles of O₂ = 21.6 moles of MgO

the atomic mass is the bottom number on the element.

-steel jelly