Step 1: Structure of Nitrogen Molecule
The nitrogen molecule (N_2) consists of two nitrogen atoms. Nitrogen atoms are highly electronegative and share three pairs of electrons to achieve a stable electron configuration.
Step 2: Bond in Nitrogen Molecule
This sharing of three pairs of electrons results in a triple bond between the two nitrogen atoms. Therefore, the bond in a diatomic nitrogen molecule is a triple bond.
Step 3: Final Answer
Thus, the bond in the diatomic molecule of nitrogen is a Triple bond.
\[
\boxed{\text{Triple bond}}
\]
From the given following (A to D) cyclic structures, those which will not react with Tollen's reagent are : 
Compound 'P' undergoes the following sequence of reactions : (i) NH₃ (ii) $\Delta$ $\rightarrow$ Q (i) KOH, Br₂ (ii) CHCl₃, KOH (alc), $\Delta$ $\rightarrow$ NC-CH₃. 'P' is : 
