How many moles of helium are 8.84×10^24 atoms of he?

14.77 mol.

Explanation:

Using cross multiplication:

1.0 mole of He contains → 6.022 x 10²³ atoms.

??? mole of He contains → 8.84 x 10²⁴ atoms.

∴ The no. of moles of He contains (8.84 x 10²⁴ atoms) = (1.0 mol)(8.84 x 10²⁴ atoms)/(6.022 x 10²³ atoms) = 14.77 mol.

i believe it is c.) 1575 j.

it's c. elements are placed in rows based on how may valencies electrons have.