If a compound formula mass was experimentally determined to be 58, the chemical formula could be?

NaCl

Explanation:

If you follow traditional rounding, Na atomic mass is 23 and Cl atomic mass 35, 23 +35 = 58.

I was taught that Cl is one of the elements you round to 35.5, but this works if you’re not in an advanced chem class.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).