Given bond orders

• For $NO$, bond order $= 2.5$
• For $NO^+$, bond order $= 3$

Relation between bond order and bond length

In molecular species, bond length is inversely related to bond order:

• Higher bond order $\Rightarrow$ stronger bond $\Rightarrow$ shorter bond length
• Lower bond order $\Rightarrow$ weaker bond $\Rightarrow$ longer bond length

Compare $NO$ and $NO^+$

Since $3 > 2.5$ the bond in $NO^+$ is stronger and shorter than the bond in $NO$.

Therefore, $\text{Bond length of } NO > \text{Bond length of } NO^+$

Check the options

• A: Bond length in $NO^+$ is greater than in $NO$ $\rightarrow$ False
• B: Bond length is unpredictable $\rightarrow$ False
• C: Bond length in $NO^+$ is equal to that in $NO$ $\rightarrow$ False
• D: Bond length in $NO$ is greater than in $NO^+$ $\rightarrow$ True

Final answer

The correct option is D.