How many elements are present in each of the following HF and. Hf ii) Co and CO iii) Si and SiO2 iv) PoCl2 and POCC3

HF and Hf consist of 3 elements: Hydrogen (H), Flourine (F) and Hafnium (Hf).Co and CO consist of 3 elements: Cobalt (CO), Carbon (C) and Oxygen (O).Si and SiO2 consist of 2 elements: Silicon (Si) and Oxygen (O). {unless you mean SI where "I" would be iodine)PoCl2 and POCC3 have 5 elements: Polonium (Po), Chlorine (Cl), Phosphorus (P), Oxygen (O) and Carbon (C).

19.948 mol.

Explanation:

Knowing that every one mole of a substance contains Avogadro's no. of molecules (NA = 6.022 x 10²³).

Using cross multiplication:

1.0 mole → 6.022 x 10²³ atoms of He.

??? mole → 12.013 x 10²⁴ atoms of He.

∴ The no. of moles of are in  12.013 x 10²⁴ atoms of He = (12.013 x 10²⁴ atoms of He) (1.0 mole) / (6.022 x 10²³ atoms of He) = 19.948 mol.