Answer:
Partial hydrogenation
Step-by-step explanation:
Vegetable oils naturally contain cis fatty acids. These fatty acids have double bonds and the two H atoms are on the same side of bond, producing a kink in the structure.
Cis fatty acids are converted into trans fatty acids by the process of partial hydrogenation or vegetable shortening. Hydrogen is added to convert some of the double bonds into single bonds but all double bonds are not removed. However, the cis double bonds end up getting converted to trans double bonds. H atoms are now on the opposite sides of the double bond. This arrangement makes the kink disappear from the structure hence trans fat is structurally similar to saturated animal fat. It increases the longevity of fats and makes it solid at room temperature but also has many side effects like increasing bad LDL cholesterol in blood.