a. TiO
b. SiO2
c. TiO3
d. MgO
Ans. c
Explanation : Certain metal oxides like VO 2, VO, VO 3 and TiO 3 show metallic or insulating property depending upon temperature, as temperature varies metalllic or insulating property varies. This is due to variation in energy gap between conduction band and valence band.