10. The graph below gives an interaction potential between two atoms as a function of
the distance between them. What sort of bonds do you expect the two atoms to have?
a. Only a single kind of strong long bond.
b. Only a single kind of weak long bond.
c. A weak long bond and a strong short bond
d. A strong long bond and a weak short bond

The given interatomic potential graph indicates that the two atoms experience a strong short‑range bond and a weak long‑range bond, so the correct option is C) A weak long bond and a strong short bond.​

Introduction: interatomic potential weak long bond strong short bond

In an interatomic potential energy curve, the shape of the graph directly reveals whether atoms form strong short bonds (like covalent or ionic) or weak long bonds (like van der Waals interactions). The question graph shows a deep minimum at a short distance and a shallow minimum at a longer distance, which corresponds to a strong short‑range bond and a weak long‑range bond between the atoms. Since shorter bonds are generally stronger and longer bonds are weaker, the correct interpretation is a weak long bond and a strong short bond.​

Concept: interatomic potential and bond strength

• An interatomic potential energy curve plots potential energy $V(r)$ versus internuclear distance $r$, and the minima of this curve correspond to stable bond distances.​

• The equilibrium bond length is at the distance where the potential energy is minimum; a deeper well (more negative energy) means a stronger bond, and a shallower well means a weaker bond.​

• In general, shorter bonds are stronger because the nuclei are closer, increasing attraction between nuclei and bonding electrons, whereas longer bonds are weaker due to reduced electrostatic attraction.​

In the given graph, the short‑distance minimum is deep (strong bond) and the long‑distance minimum is shallow (weak bond). Therefore, the atoms have a strong short‑range bond (typically covalent or ionic) and a weak long‑range interaction (typically van der Waals).​

Option‑wise explanation

Option A: Only a single kind of strong long bond

This option suggests there is just one bond type, which is both strong and long.

• A strong long bond would require a deep potential well at a large internuclear distance, but the usual relationship is that longer bonds are weaker, not stronger.​

• The graph, however, shows two distinct regions: a deep minimum at short distance and a shallow minimum at a longer distance, so it cannot be described as only a single strong long bond.​

Therefore, Option A is incorrect.

Option B: Only a single kind of weak long bond

This option claims that there is only one weak long‑range interaction, such as a van der Waals bond.

• A weak long bond corresponds to a shallow potential well at large distance, consistent with typical van der Waals forces.​

• However, the given curve clearly contains an additional deep minimum at a short distance, corresponding to a strong short bond, which this option ignores.​

Thus, Option B is also incorrect because it fails to account for the strong short‑range bond.

Option C: A weak long bond and a strong short bond (Correct)

This option matches the typical two‑component interatomic potential:

• At short distance, strong attractive forces (covalent or ionic bonding) create a deep potential well, giving a strong short bond with high bond energy and short bond length.​

• At longer distance, weaker dispersion or van der Waals forces generate a shallow minimum, giving a weak long bond with low bond energy and longer equilibrium distance.​

Because the graph shows exactly this pattern—deep well at small $r$ and shallow well at larger $r$—Option C correctly describes the bonding: a weak long bond and a strong short bond.

Option D: A strong long bond and a weak short bond

Option D reverses the physical reality and the trend visible in the curve.

• A strong long bond contradicts the general rule that longer bonds are weaker, since increased internuclear distance lowers the attractive force between nuclei and electrons.​

• A weak short bond would appear as a shallow minimum at short distance, but the curve actually shows a deep minimum there, indicating a strong bond instead.​

Therefore, Option D is inconsistent with both the graph and fundamental bond‑length–bond‑strength relationships, making it incorrect.

Key takeaway for exam preparation

When analyzing an interatomic potential graph in CSIR NET or other competitive exams, remember: short, deep minimum = strong bond; long, shallow minimum = weak bond. For this question, that pattern leads directly to Option C: a weak long bond and a strong short bond as the correct answer.​