Why must a lewis structure for a molecule be drawn before we can determine it’s molecular structure? (NEED HELP ASAP PLEASE)

The covalent compound acetylene, which is the fuel of the oxyacetylene torch used by welders, has the molecular formula c2h2. the covalent compound benzene, a commercial solvent, has the molecular formula c6h6 each of these covalent compounds contains carbon and hydrogen atoms in a one-to-one ratio. would it be correct to write the chemical formulas of each as ch? explain.

How many atoms are there in 5.70 mol of mg

The element that has the greatest electronegativity is