Match List I with List II.

(A)-(IV), (B)-(III), (C)-(II), (D)-(I)

The correct answer is option 3. (A)-(IV), (B)-(III), (C)-(II), (D)-(I).

To correctly match List I (types of defects) with List II (descriptions of those defects), we need to understand each type of defect:

A. Frenkel defect: This defect involves the dislocation of an ion (usually a cation) from its original lattice site to an interstitial site within the crystal. Hence, it's a dislocation defect.

B. Schottky defect: This defect involves missing ion pairs, meaning both cations and anions are missing from the crystal lattice, maintaining electrical neutrality. Hence, ion pairs are missing.

C. Metal excess defect: This can occur due to an extra cation being present in an interstitial site, or due to the presence of extra electrons in the crystal. Specifically, one common form is due to extra cation in interstitial site.

D. Metal deficiency defect: This defect involves the presence of fewer metal ions than the ideal stoichiometric ratio.  This can be due to cations having extra electrons, resulting in extra anion in vacant site.

So, the correct matching is 3.(A)-(IV), (B)-(III), (C)-(II), (D)-(I)