$21.$ Which of the following is a primary factor influencing the choice of refinery feedstock?

a$)$ Color

b$)$ Density

c$)$ Odor

d$)$ Taste

$22.$ What is the main effect of nitrogen impurities in refinery feedstock?

a$)$ Decreases the flash point of fuels

b$)$ Increases the sulfur content

c$)$ Reduces the efficiency of catalytic processes

d$)$ Improves the stability of refined products

$23.$ Which of the following processes is NOT involved in the production of synthesis gas?

a$)$ Steam reforming

b$)$ Partial oxidation

c$)$ Hydrocracking

d$)$ Autothermal reforming

$24.$ What is the primary use of acetylene in the petrochemical industry?

a$)$ Production of ethylene glycol

b$)$ Manufacturing of PVC

c$)$ Fuel for residential heating

d$)$ None of the above