The correct answer is option 1: hydrogen gas.

Vegetable oils are typically in liquid form at room temperature because they contain unsaturated fatty acids, which have double bonds in their molecular structure. The presence of these double bonds results in kinks in the fatty acid chains, preventing the molecules from packing closely together and remaining in a solid state.

To convert vegetable oils into solid margarine, a process called hydrogenation is used. Hydrogenation involves the addition of hydrogen gas to the vegetable oils in the presence of a catalyst (such as nickel or palladium). During this process, the double bonds in the unsaturated fatty acids are broken, and hydrogen atoms are added to the carbon atoms that were previously involved in the double bonds.

By adding hydrogen atoms, the unsaturated fatty acids are converted into saturated fatty acids, which have no double bonds and a straighter molecular structure. This allows the fatty acid molecules to pack closely together, resulting in the solidification of the vegetable oils and the formation of margarine.

Alert - correct answer should be 2: nickel catalyst