The correct answer is 1, 3 and 4 only. Key Points Carbon nanotubes These are cylindrical molecules that consist of rolled-up sheets of single-layer carbon atoms (graphene). There are single-walled nanotubes (with a diameter of less than 1 nanometer) and multi-walled nanotubes (with diameters reaching more than 100 nm). These are chemically bonded with sp2 bonds which is an extremely strong form of molecular interaction. They develop ultra-high-strength and low-weight materials that possess highly conductive electrical and thermal properties. Carbon nanotubes are promising drug delivery platforms that can be functionalized with a variety of biomolecules, such as antibodies, proteins, antigens, and DNA. Carbon nanotubes can easily penetrate cells and improve the pharmacological and therapeutic profile, and efficacy of the drug. Hence statement 1 is correct. Biotechnology facilitates the making of nanodevices using blood-compatible nanomaterials as building blocks for biomedical applications such as artificial implants including structural tissue replacements, artificial blood vessels, or functional devices such as drug delivery matrices. Using carbon nanotube as an artificial blood vessel can create blood clotting, therefore it is unsafe. Hence statement 2 is not correct. NASA has successfully demonstrated a miniaturized electronics technology with extremely high sensitivity for in-vitro detecting specific biomarker signatures, which is based on incorporating embedded vertically aligned carbon nanotubes as nanoelectrode arrays in diagnostics devices. Hence statement 3 is correct. It has been demonstrated that functionalised carbon nanotubes can be degraded by oxidative enzymes. Multiple types of microbes including bacteria and fungi have the ability to degrade carbon nanotubes (CNTs), graphene (GRA), and their derivatives. Hence statement 4 is correct.​ Important Points According to the answer key Released by UPSC, the correct answer is option C.