20. which bond is the shortest?\na. n=n\nb. c=c\nc. n≡n\nd. s=o\ne. c - c

Explanation:

Step1: Recall bond - length principle

Bond length decreases with increasing bond order. Single bonds have a bond - order of 1, double bonds have a bond - order of 2, and triple bonds have a bond - order of 3.

Step2: Determine bond - orders of each option

a. $N = N$ is a double bond, bond - order = 2. b. $C = C$ is a double bond, bond - order = 2. c. $N\equiv N$ is a triple bond, bond - order = 3. d. $S = O$ is a double bond, bond - order = 2. e. $C - C$ is a single bond, bond - order = 1.

Step3: Compare bond - orders

The higher the bond - order, the shorter the bond length. Since the $N\equiv N$ bond has the highest bond - order among the given options, it has the shortest bond length.

Answer:

C. $N\equiv N$