The intrinsic semiconductor becomes an insulator at:

CONCEPT:

Semiconductor: 

• Semiconductors are the materials that have a conductivity between conductors and insulators.
  • Semiconductors are made of compounds such as gallium arsenide or pure elements, such as germanium or silicon.
• Holes and electrons are the types of charge carriers accountable for the flow of current in semiconductors. 
  • ​Holes (valence electrons) are the positively charged electric charge carrier whereas electrons are the negatively charged particles.

EXPLANATION:

• The resistance of semiconductor materials decreases with the increase in temperature and vice-versa.
• At absolute zero Kelvin temperature, the covalent bonds are very strong, and there are no free electrons, and the semiconductor behaves as a perfect insulator.
• Hence, option 4 is correct.