In case of oxygen family (group -16) (a) The tendency for catenation decreases markedly as we go down the group (b) Maximum coordination of oxygen is four due to lack of d-orbital but that of other elements is six due to presence of d-orbitals (c) The tendency to form multiple bonds with \(\mathrm{C}, \mathrm{N}\) and \(O\) decreases as going down the group from \(\mathrm{S}\) to \(\mathrm{Te}\). (d) All are correct

Catenation plays a pivotal role in the structural diversity of compounds formed by chalcogens, the elements found in group 16 of the periodic table. Chalcogens include oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).
These elements have the unique ability to bind with themselves, leading to chains or rings as seen in sulfur's ring molecules or selenium's chain structures.

• Oxygen exhibits the least tendency for catenation due to its small size and high electronegativity that leads to strong O-O double bonds but not longer chains.
• Sulfur is known for its ability to form rings and chains, with the most common being an eight-membered ring.
• As we move further down towards selenium and tellurium, the heavier atoms have more diffuse electron clouds, which results in weaker bonds between atoms.

This diminishing tendency for catenation is attributed to the increase in atomic size and a corresponding decrease in bond energy, rendering the atoms less capable of forming stable catenated structures.

The coordination number is the total number of atoms directly connected to a central atom in a molecule or a polyatomic ion. Within group 16 elements, oxygen has a unique position due to its lack of d-orbitals. This limits oxygen's ability to expand its octet, confining its maximum coordination number to four.
For instance, in water (H₂O), oxygen is only bonded to two hydrogen atoms, but it can make up to two more bonds as seen in hydrogen peroxide (H₂O₂).

• Oxygen forms two single bonds in water, which is its most common state.
• In molecules like sulfates (SO₄^2-) and phosphates (PO₄^3-), sulfur and phosphorus reach coordination numbers of six, showcasing their ability to utilize d-orbitals.

The heavier chalcogens—sulfur, selenium, tellurium, and polonium—can go beyond the octet rule and form more than four bonds, owing to their accessible d-orbitals. This expanded bonding capacity is what leads to the varied and often complex chemistry of the heavier chalcogens.

Multiple bonding, such as double or triple bonds, is significant for the formation of stable molecules in organic and inorganic chemistry. The ability of group 16 elements to form multiple bonds with carbon (C), nitrogen (N), and oxygen (O) is a consequence of their atomic properties.
Take the example of oxygen: it forms double bonds with carbon in carbon dioxide (CO₂) and with itself in ozone (O₃), where these multiple bonds are pivotal in the stability of these compounds. In contrast, sulfur can form multiple bonds as well, as seen in sulfur dioxide (SO₂), whereas tellurium typically forms single bonds due to its lower electronegativity and larger atomic size.

• In carbonyl groups (C=O), the double bond is a significant feature found in many organic compounds like ketones and aldehydes.
• With increasing atomic number from sulfur to tellurium, the multiple bond formation ability decreases, which affects the reactivity and types of compounds these elements can form.

Due to a decrease in electronegativity and a more diffuse electron cloud, Te prefers single bonds, which is why tellurium-containing organic compounds are less common than their sulfur and oxygen counterparts. Understanding these trends helps chemists predict and synthesize new compounds with desired properties.