What are the limitations of phenolphthalein when determining if a solution is acidic

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.

Label a-f based on the table using c for concentrated and d for dilute

Name the element in group 17, period 2. (periodic table)