Question

What is the proportionality between (I) Bond length and size of atom (II) Bond length and multiplicity of bond respectively?

• A. (I)- direct (II)- inverse
• B. (I)- direct (II)- direct
• C. (I)-inverse (II)-direct
• D. (I)-inverse (II)-inverse

Hint:

Larger atoms form longer bonds; more bonds between two atoms pull them closer.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
Bond length is the average distance between the nuclei of two bonded atoms. Two things control it: how big the atoms are and how many electron pairs are shared between them.

Step 2: Part I: bond length and size of atom
Bond length is roughly the sum of the covalent radii of the two atoms. If the atoms become bigger, the sum becomes bigger. So bond length is directly proportional to atomic size. For example, the H-I bond is longer than the H-F bond because iodine is much larger than fluorine.

Step 3: Part II: bond length and multiplicity
Multiplicity means single, double or triple bond. More shared electron pairs pull the nuclei closer together. So bond length falls as multiplicity rises: C-C is 154 pm, C=C is 134 pm and the triple bond is 120 pm. This is an inverse relationship.

Step 4: Compare with options
Option (A) gives I direct and II inverse, which matches both facts. Options (B), (C) and (D) each reverse at least one relationship, so they are wrong.

Final Answer:
Bond length is directly related to atomic size and inversely related to bond multiplicity, option (A). \[ \boxed{\text{(I) direct, (II) inverse}} \]