I think ans should be VO because it's oxide show insulating property depending upon temp..

Oxide that is an insulator:

1) VO (Vanadium Oxide):
Vanadium oxide (VO) is an oxide compound of vanadium and oxygen. It is a transition metal oxide that exists in various forms, such as VO2, V2O5, and VO. Among these forms, VO is an insulator.

Explanation:
- Vanadium has multiple oxidation states, and in the case of VO, it has a +2 oxidation state.
- In the crystal structure of VO, the vanadium ions are arranged in a square pyramidal coordination with oxygen ions.
- The presence of oxygen ions forms a network of covalent bonds, resulting in a stable crystal structure.
- Due to the stable structure and the absence of free electrons, VO behaves as an insulator.
- Insulators do not conduct electricity well because they lack mobile charge carriers (electrons or ions) that can move freely within the material.

2) CoO (Cobalt Oxide):
Cobalt oxide (CoO) is another oxide compound that can act as an insulator.

Explanation:
- Cobalt oxide contains cobalt ions (Co2+) and oxygen ions (O2-).
- In the crystal structure of CoO, cobalt ions are in a close-packed arrangement, and oxygen ions occupy the octahedral holes between them.
- The ionic bonding between Co2+ and O2- results in a stable structure.
- This stable structure and the absence of free charge carriers make CoO an insulator.

3) ReO (Rhenium Oxide):
Rhenium oxide (ReO) is not a well-known oxide in terms of its electrical properties. However, it is generally considered to be an insulator.

Explanation:
- Rhenium oxide consists of rhenium ions (Re) and oxygen ions (O).
- The exact crystal structure and the bonding in ReO may vary depending on the specific oxide phase.
- In general, rhenium oxide exhibits a stable structure, and the absence of free charge carriers suggests its insulating behavior.

4) Ti2O3 (Titanium Oxide):
Titanium oxide (Ti2O3) is a compound of titanium and oxygen that can also act as an insulator.

Explanation:
- Titanium oxide has a complex crystal structure with titanium ions (Ti) and oxygen ions (O).
- In Ti2O3, the ratio of titanium to oxygen is 2:3, indicating that there is a slight deficiency in oxygen.
- The arrangement of ions in Ti2O3 results in a stable structure, and the absence of free charge carriers makes it an insulator.

In summary, VO, CoO, ReO, and Ti2O3 are examples of oxides that act as insulators. Their stable crystal structures and the absence of free charge carriers contribute to their insulating behavior.