Assertion [A] Viruses are considered to be at the borderline of living and non-living things.
Reason [R] Viruses cannot survive outside the host organism.
Assertion [A] is True and Reason [R] is True and is a correct explanation for [A].
Viruses are very small organisms which contain genetic material (DNA or RNA) and a protein coat covering it. A cellular structure is absent. Therefore viruses depend on the host for their survival. Viruses cannot survive outside the host. They can also be crystallised, which is a property of non-living things. This is the reason why they are considered to be at the borderline of living and non-living things.