What is typically involved in an addition reaction?

Correct option is D

The correct answer is (d) Atoms get added to unsaturated bonds

Explanation:
• Organic unsaturated hydrocarbons, which strictly and exclusively include chemical alkenes and alkynes, structurally contain highly reactive double or triple covalent bonds between adjacent carbon atoms.
• In a highly characteristic organic addition reaction, these chemically active multiple bonds are forcefully broken apart to structurally accommodate totally new elements.
• Subsequently, completely new atoms (such as elemental Hydrogen or reactive halogens like Chlorine) are physically and permanently added directly to the two carbon atoms that previously shared the multiple bond.
• A very common, highly important industrial example is the large-scale hydrogenation of liquid unsaturated vegetable oils to forcefully form solid saturated fats (like common vanaspati ghee).
• The general simplified chemical equation perfectly is: $CH_{2}=CH_{2} + H_{2} \xrightarrow{Ni/Pd} CH_{3}-CH_{3}$, which effectively chemically converts unsaturated compounds straight into perfectly saturated ones.

Information Booster:
• Solid transition metals such as finely divided powdered Nickel (Ni) or expensive Palladium (Pd) are extremely commonly employed as highly active catalysts to drastically speed up these specific chemical reactions.
• Fully saturated hydrocarbons (alkanes) absolutely do not typically naturally undergo addition reactions; instead, they slowly undergo totally different substitution reactions.

Additional Knowledge:
Oxidation changes without new bonding (Option a)
• This vaguely describes certain aspects of completely different Redox reactions; while an addition can certainly alter oxidation states, the main defining chemical feature is explicitly adding new atoms directly across a multiple bond.

Removal of atoms from molecules takes place (Option b)
• This specific backwards process describes a standard chemical Elimination reaction, which is essentially the exact chemical opposite of an addition reaction.

Functional groups are replaced by others (Option c)
• This exact formal definition flawlessly describes a classic Substitution reaction, extremely commonly seen mostly in saturated organic compounds.

So the correct answer is (d)