$5.$ Which of the following is a primary component of natural gas?

a$)$ Methane

b$)$ Ethanol

c$)$ Propane

d$)$ Butane

$6.$ Which petrochemical precursor is commonly used in the production of plastics?

a$)$ Synthesis gas

b$)$ Hydrogen

c$)$ Ethylene

d$)$ Acetylene

$7.$ What is the main use of acetylene in petrochemical processes?

a$)$ Fuel for automobiles

b$)$ Production of synthetic rubber

c$)$ Production of polyethylene

d$)$ None of the above

$8.$ Which of the following is NOT a petrochemical precursor?

a$)$ Butylene

b$)$ Propylene

c$)$ Diesel

d$)$ Ethylene